The Anatomy of the Domestic Fowl

THE URO-GENITAL SYSTEM — THE URINARY APPARATUS (Fig. 50 and Fig. 51). — THE MALE GENERATIVE ORGANS (Fig. 54) — THE FEMALE GENERATIVE ORGANS (Fig. 56)

The uro-genital apparatus, or apparatus uro-genitalis, consists of two groups of organs: the urinary and the genital. The former elaborate and remove the chief excretory fluid, the urine; and the latter serve for the formation, development, and expulsion of the products of the reproductive glands.

The urinary apparatus of the bird consists of two kidneys, from each of which a ureter extends and empties into the cloaca.

The Kidneys. Location.—The kidneys are located in excavations in the pelvic roof. They are related internally with the posterior aorta and vena cava, supero-internally with the lumbo-sacral vertebræ and superiorly and supero-externally with the ilium. The abdominal visceral organs lie below the kidneys. The kidneys are external to or above the peritoneum.

Shape.—In the fowl of average size the kidneys are 2½ inches long and are made up of three irregular lobes. The anterior lobe is usually the largest and the middle the smallest. The anterior border of the first lobe is located opposite the last true dorsal articulation. The anterior lobe is called the anterior pelvic or ilio-lumbar lobe, the middle the middle pelvic or ilio-sacral lobe, and the posterior the posterior pelvic lobe.

Structure.—The whole kidney has a fine transparent covering. The dark, brownish-red parenchyme can be seen through this membrane. It has a blood vascular system and a urinary tubular system. The larger arteries, the veins, and the nerves pass between the lobules, and the smaller vessels between the tubules. These form fine network or plexuses. The lymphatic vessels are very few, and are mainly found on the surface. The kidneys are pierced in their posterior third by the external iliac artery and at about its middle by the venous branches forming the posterior vena cava.

The lobes are made up of lobules, which are plainly perceptible from the external surface. Each lobule is apparently a unit within 170itself. It receives its blood supply from small branches of the renal artery and is made up of a cortical or peripheral portion which contains the glomerules (Fig. 52, A) and a medullary portion, which is made up of tubules, or urinary canals, arteries, veins, and nerves.

Fig. 50.—Photograph showing spinal cord and relative positions of the kidney, lung and heart. 1, Heart. 2, Lung. Note the indentations made by the ribs. 3, The anterior, middle and posterior lobes of the kidney. The lobules are plainly visible. 4, The lumbo-sacral segment of the spinal cord. 5, Terminal cord filament. 6, The cervico-dorsal segment of the spinal cord. 7, The brachial nerve plexus. 8 and 9, The lumbo-sacral plexus. 8, The ischiadic nerve. 9, The lumbar nerves.

The urinary canals are divided into two kinds, namely, the outer and the inner tubular systems. The outer canals, called the tubulæ uriniferi corticalis, are very small in caliber and are located in the 171lobules. The renal artery (Fig. 53, No. B, 3) breaking up into arterioles in the kidney, and finally reaching the cortical portion of the lobules, form capillary plexuses in the shape of minute spheres, which are the glomerules (Fig. 53, No. C, 3 and B, 5). Around each glomerule there is formed a capsule called Bowman’s capsule, which is the beginning of the uriniferous tubule. This entire mass is called the Malpighian body, or renal corpuscle. This capsule then extends as the urinary, or secreting tubule, being at first constricted, then convoluted, and terminates into a second portion, the descending limb of Henle. This portion of the tubule becomes constricted. It then forms the loop of Henle and ascends as the second portion, or second limb of Henle, which is again of greater diameter. The top of the secreting tubule is slightly wavy and empties into the collecting tubule along with many others. These collecting tubules in turn merge into large tubules which finally empty into the ureter (Fig. 53, No. 14). These collective bundles correspond to the pyramids of the kidneys of mammals.

Fig. 51.—The kidneys. 1a, The posterior. 1b, the middle and 1c, the anterior lobes of the kidney. 2, The posterior aorta. 3, The external iliac or crural artery. 4, The ischiadic artery. 5, The sacralis media artery. 6, The ureter which empties into the cloaca at 7. 8, The external iliac vein. 9, The internal iliac vein. 10, The iliacus communis.

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Fig. 52.

A. Photomicrograph of a section of a kidney showing three lobules. 1, Cortical portion of lobule showing glomeruli. 2, The central or medullary portion of the lobule. 3, The outer surface of the kidney.

B. Salts from the urine of a hen. 1, Uric acid crystals. 2. Sodium urate crystals.

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Fig. 53.—The renal structure.

A. 1, Capillary blood-vessel. 2, Descending limb of Henle. 3, Collecting tubule. 4, Ascending limb of Henle.

B. 1, Branch of renal artery. 2, The descending or medullary branch. 3, The ascending branch. 4, The arteriole taking part in the formation of the glomerule. 5, The glomerule. 6, Bowman’s capsule. 7, Blood-vessel extending from the glomerule. 8, The vein of the medullary part of the lobule. 9, The neck. 10, The convoluted tubule. 11, The descending limb of Henle. 12, Henle’s loop. 13, The ascending loop of Henle. 14, The collecting tubule.

C. 1, Section through a convoluted tubule. 2, Bowman’s capsule. 3, The glomerule.

The neck of the uriniferous tubule as it emerges from Bowman’s capsule is short and narrow and is lined with a few cuboidal cells. Toward the glomerular end the cells are of a transitional form gradually merging into the flat squamous type peculiar to Bowman’s capsule. The first convoluted tubule is lined with irregular cuboidal or pyramidal epithelial cells. The descending limb of Henle’s loop is narrow and is lined with a simple layer of flat epithelial cells. In the loop the epithelium changes from the flat type in the descending limb to the cuboidal in the ascending limb. The ascending limb of Henle’s loop again becomes broader and is lined with low cuboidal cells. The second convoluted, or tortuous, tubule is lined with low 174cuboidal cells as are also the collecting tubules. The collecting tubules originate from every part of the internal substance of the lobules, and extending to the gyrations, uniting in the pinniform structure and traversing to the margin of the lobules, following along the uneven surface, infero-laterally and toward the median body line, finally empty into the ureter.

There are many arterial branches given off from the arteria renalis. The arteries which supply the kidneys are given off from the posterior aorta and ischiadic artery. As soon as these arteries enter the kidney they break up into two systems. One system supplies the kidney substance with nourishment in the form of nutrient blood; the second system supplies the glomerules with what may be considered functional blood (Gadow). The second system of arteries branches into the small arteria interlobularis, which pass between the lobules of the kidneys where they give off side branches which penetrate the cortical portion of the lobules and form the capillary plexus, the glomerule.

The arteriole that enters into the structure of the glomerule is lined with endothelial cells and is surrounded by a few muscle fibers and a fine network of connective tissue. The vessel that carries the blood away is similarly constructed.

Function.—In the glomerules the liquid portion of the urine is filtered out of the blood, which urine flows through the uriniferous tubules and passes from the kidney through the ureter. In the cubical cells are extracted the solid portions of the urine which also pass through the tubules with the liquid. The urinary secretion, as found in the ureter, does not contain much liquid, but, on the contrary, is made up of a pasty material consisting of salts which are, for the most part, uric acid crystals and sodium urate (Fig. 52, B). This material becomes hard, like cement, soon after being exposed to the atmosphere. This secretion may be noted as a whitish pasty material on the outer parts of the feces, or droppings, voided by the birds.

The Ureter. Location.—The ureter extends along the inferior surface of the kidney. It has its origin near the anterior extremity of the kidney, and passing posteriorly the entire length of the kidney receives tributary collecting tubules, and terminates in the upper wall of the cloaca in the urodeumal portion.

Shape.—The ureter gradually enlarges in diameter until it reaches 175the posterior border of the kidney, and then maintains about the same caliber throughout the rest of its course.

Structure.—The ureter wall is made up of three coats as follows: mucous, muscular and fibrous.

Function.—The ureters serve as a passage way for the urine from the kidneys to the cloaca.

The male generative organs in the fowl consist of two testicles and an excretory apparatus, the vas deferens, for each.

The Testicles. Location.—The testicles are located in the sublumbar region of the abdominal cavity, behind the lungs, below the anterior extremity of the kidneys, and opposite the last three ribs.

Fig. 54.—The pelvic organs of a cockerel. A, Testes. B, Rectum. C, Cloaca. D, Vas deferens. E, Kidney. F, Adrenal gland. G, Lungs. H, Ureter.

Shape.—The testicles are ellipsoid in shape; their size varies with the different species of birds. The two in the same bird are usually of the same size, though one testicle may be slightly larger than the other. In a summary of a large number of weights of the testicles of ten months old cockerels, the average weight was 0.021 pound each. The average measurements were 2 inches in the major diameter and 1 inch in the minor diameter. In the cockerel before sexual maturity, which is denoted by the male bird’s crowing, the testicles are very small. They resemble, in shape, a navy bean and are yellowish-white in color.

176Structure.—The testicle is surrounded by a thin fibrous capsule, which, in the mature cock, is very vascular. This capsule sends into the interior of the gland, septa which form the framework, or supporting structure. This framework forms the spaces in which are located the glandular substance. The glandular portion consists of the tubuli seminiferi, which are lined with cubical cells. The framework supporting these tubules gives passage to arterial branches of the spermatic artery, which furnish an abundant blood supply; the framework also supports the veins returning the blood from the testicle. The seminiferous tubules end in blind extremities in the epididymus or globus minor, and unite in the seminiferous canals. All arteries, veins, lymphatics, and seminiferous tubules enter or leave through the globus minor at the attached portion of the testicle. The epididymis is made up largely of convoluted tubules which are the continuation of the secreting tubules of the globus major. The walls of the tubules of the globus minor become thicker and are provided with smooth muscle cells in addition to the connective tissue and endothelial lining. The convoluted tubules empty into the vas deferens. The epididymus is covered by the fibrous capsule; which corresponds to the tunica albuginea of mammals and may be considered as a reflection or modification of the visceral peritoneum.

The substance of the testicle is very soft; in fact, it may be said to be of the consistency of encephaloid material. It is made up of secreting tubules in which are found the spermatozoa; it also contains cells which produce an internal secretion, or hormone. There is also produced some fluid in which the spermatozoa float, the whole material manufactured constituting the semen.

The spermatozoa of the fowl are provided with long cylindrical bodies, which may be straight or wavy (Fig. 55, A). The body of the spermatozoon is obtuse anteriorly, and posteriorly, tapers into a filimentary tail, or flagellum, of varying length, by the aid of which the spermatozoon moves about in the fluid.

The histological structure of the testicles of the baby chick at hatching is approximately one-half white fibrous connective tissue. The seminal tubules are small and widely distributed among the connective tissue. The cells of these tubules possess rather large nuclei, round in shape, with linin network and chromatin granules, typical of resting germ cells. As the bird develops the testicles grow, the seminal tubules become larger, and the amount of connective tissue correspondingly less.

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Fig. 55.

A. Spermatozoa of a cock. a, The spermatozoa. b, The head. c, The tail.

B. The oviduct of a hen removed. A, The oviduct. B, The superior ligament. C, The inferior ligament. Note the oviduct thrown in folds and the anastomosing blood-vessels.

178In addition to the tubules, the spermatogenic cells, and the connective tissue, there is also in the testicles more or less fat. There is a small amount of connective tissue between the seminiferous tubules, in which locations there are also clusters of polyhedral cells, with round nuclei, others are the interstitial cells.

The Vas Deferens (Fig. 54, D). Location and Shape.—Extending from the epididymus, is the vas deferens which runs backward on the infero-internal surface of the kidney and to the outside of the ureter. It is very tortuous passing on the infero-lateral surface of the kidney in company with the ureter and becoming somewhat expanded posteriorly it terminates in the upper wall of the cloaca in a rather small papilla located in the uro-genital portion of the cloaca anterior to the mouth of the ureter. This papilla is the organ of copulation and in ducks is very large, and spirally elongated, and retractile forming a kind of penis. The papilla is traversed by a furrow on the upper surface through which the semen flows.

Structure.—The vas deferens is covered and supported by the peritoneum. Its wall is made up of a fibrous structure in which may be found smooth muscle fibers. The wall does not possess glands. It is lined with columnar epithelium. The posterior end is expanded and terminates into a papilla. The base of the papilla is surrounded by a plexus of arteries and veins, which serve as an erectile organ during the venereal orgasm, when the fossa of the turgid papilla is everted, and the semen brought into contact with the similarly everted orifice of the oviduct of the female, along which the spermatozoa pass by undulatory movements of their ciliary appendage, or tail.

The female generative organs consist of one ovary and an oviduct.

Location.—The ovary is located similarly to the testicles of the male bird, in the sublumbar region of the abdominal cavity, just at the anterior end of the kidneys, posterior to the lungs, and slightly to the left of the center.

Shape.—In the pullet the ovarian mass appears somewhat like a bunch of grapes, being made up of from 3500 to 4500 small, whitish spheres, which represent the undeveloped ova, and which in the 179active state are developed, one by one, into yolks with their blastoderms. From the blastoderm the fetus may later be developed. In the active ovary of the laying hen the ovarian mass is of considerable size, as it contains ova in different stages of development. Only one ovum is completely developed at a time, though occasionally there may be only a few hours between the maturity of successive ova. The ova receives nourishment from the blood-vessels of the capsule, which vessels are branches of the ovarian artery.

Fig. 56.—Functionating female generative organs of a hen. 1, Ova in process of formation of yolk. 2, Stigmal line at which point the capsule ruptures when ovum is mature. 3, The funnel end of the oviduct. 4, The oviduct torn loose and laid to one side, the albumin-secreting portion. 5, The shell membrane secreting portion. 6, The albumin. 7, The yolk. 8, The shell-secreting portion. 9, The cloaca. 10, The rectum.

Structure.—The ovary contains very vascular cellulofibrous tissue. The ovum as it develops is attached to the ovarian body by means of a delicate white fibrous pedicle. When the yolk is mature it escapes from the enveloping fibrous capsule by a cleavage of the capsule. The cleavage line is called the stigmen (Fig. 56, No. 1802). The yolk is surrounded by a very delicate membrane called the vitelline membrane. The empty sac now shrinks and finally disappears.

The Egg.—The principal divisions of the egg are the yolk, the albumin outside of the yolk content, the shell membranes and the shell (Fig. 58). As stated, the yolk is formed in the ovary, leaving the other three portions to be formed in the oviduct.

Fig. 57.—Section through the ovary of the hen. a, The ova. d, An ovum beginning to receive deposits of yolk material. c, Ova farther advanced in yolk formation.

The albumin may be subdivided into, first, a thin layer of albumin lying close around the yolk; second, a thick layer of albumin lying at the outer periphery; and third, a modification of the albumin called the chalazæ. The chalazæ are twisted, dense cord-like structures at either pole of the yolk, one end of which is adherent to the vitelline membrane and the other to the inner membrane surrounding the albumin. The chalazæ thus act as stays to this structure, which is carrying a delicate burden, the blastoderm.

181The shell membrane consists of two layers, an inner delicate, and an outer thicker layer. When the egg is just laid these two membranes are in all parts closely adherent to each other, and the egg content completely fills the shell cavity. As soon as the content cools there is a slight contraction; the two shell membranes separate at the large end of the egg, forming an air cell which gradually enlarges as the evaporation of liquid through the pores of the shell takes place.

Fig. 58.—A diagram of the parts of the egg. a, The blastoderm. b, The shell. c, The outer shell membrane. d, The inner shell membrane. e, The air-sac at the large end of the egg. f, The albumin. g, The chalaza. h, The yellow layers of yolk. i, The white layers of yolk. k, The flask-shaped portion of white yolk. l, The vitelline membrane.

The shell consists of several layers. Three are easily distinguishable: first, an inner mammillary layer, consisting of minute conical deposits of calcareous material; second, a middle spongy layer, composed of a thick network of fibers; third, an outer delicate, cuticle-like structure. In certain breeds of poultry a pigment may be added; for example, in ducks a pea green, in turkeys a spotted brownish material, and in fowls pink and various shades of brown. The egg shell is porous to admit the free exchange of air during the process of incubation.

An average sized hen egg weighs about 2 ounces, of which 11 per cent. is shell, 32 per cent. yolk, and 57 per cent. white. The principal chemical constituents of the egg are as follows: ash, or mineral matter, 9 per cent.; fat, or hydrocarbon, 9.3 per cent.; proteids, or nitrogenous matter, 11.9 per cent.; and water, 65.5 182per cent. There is apparently no constant proportion of weight between the yolk and albumin. There is also a variation in the weight of the shell due to its variation in thickness.

In an examination of ten eggs of average size, the yolk constituted 31 per cent. of the total weight of the egg.

The following is the result of the analysis of twelve eggs of average size. This analysis included the shell and all other parts taken together.^[6]

The Oviduct.—The three separate and distinct portions of the egg, albumin, shell membranes, and the shell, are constructed in different parts of the oviduct.

Location.—The oviduct of the hen extends along the left side of the bodies of the vertebræ, and the roof of the pelvic cavity and lies dorsal to the abdominal air-sac. It extends from the posterior border of the ovary and empties into the cloaca (Fig. 56, No. 3 and 8) through a transverse slit.

Shape.—In a well-developed Plymouth Rock pullet, but one whose reproductive organs have never become active, the oviduct is about 4½ inches long; in the fully developed and active state it is from 18 to 20 inches long, and in a collapsed state about ½ inch in diameter. It is held in position by two ligaments, a dorsal and a ventral (Fig. 55, B) to be described later. The oviduct is tortuous in its course, forming three principle convolutions before reaching 183the cloaca, and like the ovarian mass, in its active state, pushes the abdominal viscera downward and toward the right side.

Structure.—The oviduct consists of three coats: first, the serous, located on the outside, which is a reflection of the peritoneum; second, the muscular middle tunic; third, the mucous coat, which in a resting state is thrown into folds.

Fig. 59.—The active oviduct of a hen laid open. 1, The ovary. 2, The funnel. 3, The albumin-secreting portion. 4, The isthmus. 5, The shell=gland portion. 6, The vagina. 7, The superior ligament. 8, The inferior ligament.

Parts of the Oviduct.—The parts of the oviduct are as follows: the funnel, the albumin-secreting portion, the isthmus, the shell-gland portion, or uterus, and the vagina (Fig. 59).

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Fig. 60.—The mucous lining of the oviduct.

A. Transverse section of the oviduct wall in the region of the neck of the funnel showing primary and secondary folding of the epithelium (after Surface).

B. Showing the type of gland cells of the funnel region.

C. Transverse section through the wall of the uterus showing the deep folds.

D. Section from the albumin-secreting portion showing the opening of a tubular gland and also showing the character of the cells.

The funnel is the trumpet-shaped portion, the ostium tubæ abdominale, whose mouth or fimbriated opening faces the ovary, and lies ventrally to receive the ovum, or yolk, as it is discharged from the ovary. Its thin wall, expanded in the anterior portion, is provided with fimbriæ-like projections. This funnel-shaped portion soon converges to form a constricted portion. This portion of the active oviduct is from 3 to 4 centimeters long. The mucous membrane occurs in folds forming low longitudinal spiral ridges (Fig. 60, A). The fimbriæ are continuous with the dorsal and the ventral ligament of the oviduct; and from this point, where the ridges of the mucous membrane are almost nil, they gradually increase in height as they extend down the tube. These ridges are continued in those of the second, or albumin-secreting portion (Fig. 60, D). At this point they increase in height very rapidly. Here the bundles of muscular fibers of the middle coat are thin and distributed among bundles of connective tissue. The muscular fibers consist of two layers, an outer longitudinal and an inner circular. At places in this portion the inner bundles may be noted to extend longitudinally. In embryological development the epithelial layer has an origin different from the outer layers of the oviduct. In the fetal development the Müllerian duct arises as a thickening along the Wolffian body just ventral to the gonad. This Müllerian duct is at first a solid cord of cells. It later develops a lumen, and grows posteriorly until it connects with the cloaca. At the time of this posterior growth, mesenchyme cells migrate in from the surrounding tissue and form a layer about the duct. From this layer of mesenchyme cells there are developed the outer 185layers of the oviduct, which layers later develop the muscular structure and the connective tissue. The epithelium and its derivatives, which represent the glandular structures, are formed from the walls of the old Müllerian duct. Thus the two sets of tissues, having different origins, likewise have different functions. The epithelium is concerned entirely with secretion, and the derivatives of the mesenchyme are concerned with supporting and muscular function.

Fig. 60. A.—The mucous lining of the oviduct.

E. Section of the epithelium from the vagina showing unicellular glands.

F. A section from the isthmus showing opening of a tubule.

To summarize, six layers of tissue occur in the funnel region, namely, an outer serous covering, an outer longitudinal muscular layer, a layer of connective tissue, an inner circular layer, a second layer of connective tissue, and an inner mucous layer. The mucous layer is made up of glands, as follows. The unicellular glands occur between the ciliated cells of the epithelium. These glands are found only in the posterior half of this division of the oviduct. The glandular grooves are made up of an accumulation of gland cells at the bottom of the grooves between the secondary folds of the epithelium. These are found in all parts of this division except the extreme posterior part. In the posterior part we find the third type of glands, the tubular variety.

The second division of the oviduct, as stated above, is the albumin-secreting portion. The funnel division gradually merges into the second portion. These two portions are distinguishable from each other. The walls of the albumin-secreting portion are much thicker and the longitudinal ridges are higher. This section is the longest of the five divisions, measuring from 40 to 42 centimeters in length, or more than half the length of the oviduct. The albumin division terminates rather abruptly into the third division, the isthmus (Fig. 59, A).

186It is probable that the secretion of albumin is not confined to the cells of the second division; yet we are safe in saying that the major portion is formed here. The folds of mucous membrane in this division are thicker and higher than in the funnel, due to their containing cells of the high columnar type, and to the fuller development of the glands which are of the tubular variety. The muscular layer is heavier, and therefore the muscular power to force along the tubes’ contents is greater. In the formation of the mucous folds we find, in transverse sections, that the central core is made up of connective tissue which carries blood-vessels and nerve filaments, as in other similar glandular structure. The epithelium contains glandular cells of two varieties, namely, the ciliated, columnar variety, and the unicellular, goblet variety (Fig. 36, No. B, 2). These two kinds of glandular cells are rather evenly distributed throughout the epithelium of this section of the oviduct. The unicellular gland cells are more numerous at the mouths of the ducts leading from the tubular glands. The nuclei of the ciliated cells are oval and lie near the middle of the cells or a trifle toward the base from the middle. The protoplasm of the cells is finely granular. Strong cilia in considerable number surmount each cell. In some cases the goblet or mucous cells have pushed apart the ciliated cells, and their prolongations extend farther than the surface of the ciliated cells. The nuclei of the goblet cells are round, and lie nearer the proximal end than those of the ciliated cells.

The third division of the oviduct, the isthmus, continues from the albumin-secreting portion and terminates in the expanded portion called by some anatomists, the uterus. Toward the posterior end of the albumin-secreting portion the longitudinal folds of mucous membrane become lower, making, at the juncture of this and the isthmus, a clear fine of demarcation. For a distance of 2 or 3 centimeters the folds are low, after which they gradually become higher, but never reach the height or thickness of those in the albumin-secreting portion.

The clear-cut line between the albumin-secreting portion and the isthmus is partly due to a zone in which the long tubular glands are lacking. The core of the folds of mucous membrane in this zone contain much more connective tissue. The cells are both ciliated and unicellular. The rest of the histological structure of the isthmus is the same as that of the albumin-secreting portion.

187The function of the isthmus is to secrete, or to form, the shell membrane, the membrana testacea.

The fourth division of the oviduct is the uterus, or the shell-gland portion (Fig. 60, C). There is no clear line of demarcation between the isthmus and shell-gland portion, the walls gradually expanding. In this region the folds of mucous membrane become leaf-like and of considerable length, extending into the lumen, thus affording a greater cellular surface. The same coats of the duct are present here as in other parts; but the outer longitudinal muscular layer is thicker and possesses more strength. The quantity of connective tissue is about the same. The glands are of a tubular type and the same two varieties of epithelial cells are found here as elsewhere, namely, the ciliated high columnar and the unicellular mucous variety.

In the active glandular cells of the shell-forming region the nuclei are small, dark staining, and lie toward the center of the cell. The chromatin granules and nucleoli take on a comparatively deep basic stain, but they do not show the intense stain found in the albumin and the isthmus region. The cytoplasm of the uterine tubular glands does not present as heavy a granular appearance as that of the albumin portion. These cells are diffusely granular, the granules appearing of one size and taking the stain faintly. The function of this portion is to secrete, or form, the hard calcareous covering which has been described at the beginning of this section.

The fifth division of the oviduct is the vagina. There is located, at the juncture of the shell-gland portion with the vagina, a strong sphincter muscle. The vagina is that constricted portion of the oviduct extending from this muscle to the cloaca. The mucous membrane forms low narrow folds with secondary folds, which appear continuous with those of the shell-gland portion. The core of these folds is composed of connective tissue. The vagina in the hen of average size measures from 12 to 13 centimeters long (Surface). The inner or circular muscular layer is well developed; it is much thicker than in any other part of the oviduct. This extra development gives the power necessary to successfully expel the egg. The outer longitudinal layer is not so well developed; its bundles are scattered throughout the connective-tissue layers. The egg is caused to move along in the oviduct by a successive series of contractions of the circular muscular fibers posterior to it. There are no tubular glands in this portion, but a simple layer of high 188ciliated columnar epithelium, and some goblet, or mucous cells. The cells on the surface generally are long and slender; in the grooves between the mucous folds the cells are shortest, reaching their greatest length at the tops of the folds.

The function of the vagina is the secretion, or formation, of the outer shell cuticle commonly called the bloom, and also in certain breeds, as indicated above, the tint.

The cloaca furnishes a passage way from the vagina to the external world by way of the anus. The walls of the cloaca contain glands.

The Ligaments of the Oviduct.—It is held in position by two ligaments, one dorsal and one ventral. The dorsal ligament of the oviduct is formed by a double layer of peritoneum with a very small amount of connective tissue interposed. The peritoneum is also reflected over the oviduct. The ventral ligament of the oviduct is narrower than the dorsal, but is similarly constructed. Both ligaments are rather veil-like in appearance. During the first four or five months of the growth of the young female fowl the development of the oviduct and its ligaments is in proportion to that of the body. With the elongation that takes place about the time of functionation, as described above, the ligaments enlarge in proportion to the enlargements of the oviduct. The dorsal ligament maintains a line of attachment to the body wall from the caudal end of the body cavity to the fourth thoracic rib. The ventral ligament elongates only slightly during this developing period. It becomes thicker and stronger and early develops a muscular coat. It also grows in width except at the caudal end. At this point the ligament is simply a mass of muscular tissue of the smooth or involuntary type. These ligaments are fan-shaped.

The muscle fibers of the dorsal ligament of the laying hen, have their origin in a line near the medial side of the dorsal margin. At this point the bundles of fibers are quite thick, but are spread out thinly toward the margin of the oviduct. Frequent anastomoses are noted. The muscular fibers become continuous with the circular ones of the oviduct.

The ventral ligament of the oviduct of the laying hen is largely a muscular cord 3 to 6 centimeters in diameter. The caudal end is thicker, becoming gradually thinner toward the anterior portion. The bundles of muscular fibers extend toward the oviduct blending with the circular fibers of that viscus. The ligaments terminate 189anteriorly in such a manner that they aid in forming the serous ovarian pocket, which guides the yolk into the fimbriated portion, or funnel, of the oviduct. The walls of the ovarian pocket are formed by the left abdominal air-sac, a part of the intestine, and the mesentery. The dorsal portion is formed by the roof of the abdominal cavity, and the ventral portion is formed by the dorsal wall of the air-sac. The medial, the anterior, and the lateral limit of the pocket are formed by a fusion of the wall of the air-sac to the mesentery and to the body wall. Posteriorly, the wall consists of the transverse part of the small intestine and the caudal portion of the left cæcum with their attached mesentery.

THE DUCTLESS GLANDS

These glands do not possess excretory ducts. They furnish materials which are added to the blood or lymph as it passes through them. The material from each gland is known as an internal secretion, or hormone. Some of these secretions are powerful materials and influence profoundly the body nutrition. The ductless glands are usually given as follows: the spleen, the lymph glands, the pineal gland, the pituitary body, the thyroid gland, the thymus gland, the adrenal glands, and the parathyroids. The spleen, the pituitary, the pineal, and the lymph glands are described in other sections.

The Thyroid Gland (Fig. 21, No. 16). Location.—The thyroid gland lies on the ventral side of the carotis communis at a point where the carotis communis touches the jugular vein, which is about the point of origin of the vertebral artery.

Shape.—The thyroid gland is small, oval or somewhat roundish, and red or rose-colored.

Structure.—The thyroid gland has a fibrous capsule, which sends into the interior septa which divide it into acini. These acini are closed and contain a fluid. The thyroid is a ductless gland. Short arteries from the carotis enter this gland, and some large veins connect it with the jugular vein. The lymph vessels which lie along the neck are closely connected with it and receive twigs from the gland. The minute lymphatic capillary endings are found in its septa and in its capsule. The acini are lined with a single or a double row of cuboidal secreting cells. There are two kinds of cells, namely, secreting and resting cells. The actively secreting cells secrete colloid.

The parathyroids consist of two small bodies attached to the lower pole of the thyroid.

The Thymus Gland (Fig. 47, No. 10).—The thymus gland is an organ of fetal and early baby chickhood. It soon undergoes retrogressive changes into fat and connective tissue. It is of epithelial 191origin, being formed in fetal life from the entodermal cells of the dorsal end of the throat fissure.

Location.—The thymus gland lies anterior to the thyroid, the latter lying the deeper.

Shape.—The thyroid consists of two lobes, which are united by connective tissue, and appears as a loop-like acinous gland lying along the neck and near the region of the bronchi and the jugular veins with fibrous extensions toward the head.

Structure.—The gland lobes are divided into lobules, which consist of a cortical and a medullary portion. The cortex consists of nodules of compact lymphatic tissue similar to those found in the lymph glands. These occupy the chambers formed by the septa of connective tissue. In the medulla there are a number of spherical, or oval bodies composed of concentrically arranged epithelial cells. These are known as Hassall’s corpuscles, and represent only the remains of the original glandular epithelium. They are characteristic of the thymus gland. The thymus appears to be a type of lymph organ. Lymph vessels are rare; a few blood-vessels on the upper side form capillary nets.

The Adrenal Gland (Fig. 54, F). Location.—The adrenal gland, often called the suprarenal capsule, lies just anterior to the front part of the anterior lobe of the kidney, adjacent to the testicles in the male and to the ovary in the female. It is loosely attached by connective tissue to the posterior aorta and to the vena cava.

Shape.—It is yellowish-brown or reddish-pink in color, small, and of irregular formation.

Structure.—The adrenal gland consists of a cortical and a medullary portion, although these two parts are not distinctly marked. The cortical portion has columns which extend deeply into the gland, and the medullary portion sends columns into the cortical portion. Therefore, the two substances, lying side by side, form a cord-like structure.

It is probable that the cortical portion is derived from the ingrowths of the peritoneum, and the medullary cords from the sympathetic ganglion.

The cells are cylindrical or polygonal in shape, with an eccentric substance between the columns. The cords, or columns, form between them, elongated channels which extend into the interior of the gland and end as blind or cæcal extremities. Large ganglionic nerve cells belonging to the sympathetic system occur near the surface 192of the gland. The blood-vessels are not well developed in the interior of the gland but are numerous and of good size in the outer parts. Lymph vessels are also present.

Function.—The adrenals are ductless glands. They secrete an internal secretion, or hormone, which influences the tonus of the blood-vessels. An extract from these glands is called adrenalin.

THE RESPIRATORY APPARATUS (Figs. 50 and 61, A )

Owen says: “Notwithstanding the extent and activities of the respiratory function in birds, the organs subservient thereto manifest more of a reptilian than of the mammalian type of formation.”

By the action of the respiratory organs certain chemical and physical changes take place in the blood. The chief of these consists in absorption of oxygen from, and giving off carbon dioxide to, the atmospheric air, the former changes being necessary for the elaboration of the fluid, the latter for the elimination of a substance which, if retained, would prove injurious. The organs of respiration are invariably adapted to the wants of the animal and the medium in which it lives.

In the bird, which breathes through its nose, the organs of respiration are nostrils, nasal chambers, pharynx, superior larynx, trachea, inferior larynx, bronchi, bronchial tubes, lungs, and air-sacs.

The Nostrils and the Nasal Chambers.—The nostrils of the bird open externally by two small elliptical openings, which pierce the upper mandible. Within each nasal chamber (Fig. 26, A) are three turbinated laminæ, or turbinated bones. The inferior one is a simple fold adhering to the lower and anterior part of the nasal septum. The middle turbinated bone is the largest. It is of infundibular form, and adheres by its base to the septum and externally to the side wall of the nose. It is convoluted with two and a half turns. The superior bone, of bell shape, adheres superiorly to the frontal bone. The internal turbinated bone extends toward the orbit; the external terminates in a cul-de-sac behind the middle turbinal (Fig. 26, No. A, 1 and 2, and G).

The nostrils are separated by a partition which is partly bony and partly cartilaginous. The posterior nares is represented by a long slit in the hard palate.

The Pharynx and the Superior Larynx.—A transverse row of horny, filiform papillæ marks the anterior border of the pharynx, where in other animals the soft palate, or velum, is located. (For further description of the pharynx see special chapter.)

The supero-posterior border of the larynx, at the juncture of the 194larynx and the esophageal margin, is marked by a second transverse row of horny, filiform papillæ, which point backward. There is no epiglottis. The superior part of the larynx is pierced by an oval, slit-like opening, the glottis, which is provided with two lips. These when brought together, tightly close the glottis so that nothing can fall through into the larynx in the act of deglutition. The margin, or rim, of this opening is called the rami glottis. The glottis is controlled by two pair of muscles.

The superior surface of the larynx is somewhat triangular with the apex directed forward. A few delicate, filiform papillæ are upon its surface. The bird has, as already indicated, two larynxes, the superior larynx located at the upper end of the trachea, and the inferior larynx at the bifurcation of the trachea. The inner surface of the superior larynx is smooth and does not contain vocal cords; it is in these animals simply a passage for air. It is joined to the trachea inferiorly by a ligament, the crico-trachealis, and lies at the base of the tongue supported by two cornua of the os hyoideum.

The cartilages forming the principal support of the superior larynx, consist of four pieces, as follows: one unequal ventral piece, two side pieces, and one unequal dorsal piece. The cartilaginous, flat, ventral cricoid, early in the bird’s life, often becomes bony. The side pieces are separated from it, only exceptionally fusing with it. The dorsal cricoid piece also often becomes bony. The two arytenoid cartilages, joined with the cricoid superiorly, are three-sided, and are united to each other in a sharp angle. They form the superior opening of the superior larynx.

The Trachea.—The trachea is cylindrical and varies in length in different kinds of birds in accordance with the length of the neck. It consists of from 90 to 120 cartilaginous rings, complete with the exception of the two uppermost, which rings are held together by intercartilaginous ligaments. The tracheal rings are constructed of hyaline cartilage and the ligaments of fibrous tissue. It is lined with a mucous membrane covered by columnar epithelium. The trachea is a passage for air alone and terminates in the inferior larynx.

The Inferior Larynx.—The inferior larynx, called the true larynx because it is the organ of voice, is located at the inferior end of the trachea and the superior ends of the bronchi. By some anatomists this organ has been called the larynx broncho-trachealis. The larynx is flattened laterally in fowls. It contains two membranous folds, 195which in the production of sound are caused to vibrate. These folds are half-moon shaped elastic structures, located in the bony, arrowlike way, intero-inferiorly. These structures are called the membrana tympana interna. In the duck this inferior larynx is represented by a drum-like cartilaginous and bony structure, called the bulla tympaniformis. This bulla is a resonant apparatus which serves to strengthen the voice.

In song birds there is a double glottis, usually produced by a bony bar, called the pessulus, or os transversale, which traverses the lower end of the trachea from front to rear. It supports a thin membrane which ascends into the tracheal area, and, terminating there by a free concave margin, is called the membrana semi-lunaris. This is most developed in singing birds, and being vibratile, forms an important part of their trilling vocal apparatus. The air passes on each side of the membrana semi-lunaris and its sustaining bone to and from the bronchi and lungs.

The last ring of the trachea usually expands as it descends, with its fore and posterior parts produced, and the lower lateral borders concave; the extremities of the pessulus, butts against the angle thus formed and expands to be attached, also with the fore and posterior terminations of the first half ring of the bronchus, strengthening and clamping together the upper part of the vocal framework. The second bronchial half ring is flattened and curved with the convexity outward, like the first, but is more movable. The third half ring is less curved and further separated from the second, to the extremities of which its own are connected by a ligament, and, for the intervening extent, by a membrane; its inner surface supports the fibrous cord, or fold, which forms the outer lip of the glottis of that side; it is capable of rotary movements on its axis, and is an important agent in the modulation of the voice. All these parts just described are bony.

The Bronchi and the Lungs.—The bronchi, two in number, are provided with only incomplete cartilaginous rings. They enter the inferior face of the lungs, toward their anterior and middle thirds and break up into primary bronchi, which give off at right angles, secondary bronchi, and these latter in turn give off tertiary branches.

196

Fig. 61.—The lung.

A. The outer surface of one lung. Note the flattened oval shape. It is not divided into lobes. 1, The bronchus. 2, Primary tubules showing openings leading from the primary tubules to the secondary tubules. 3, Openings of two of the large tubes into the diaphragmatic and abdominal air-sacs.

B. Sectioned surface of lung. 1, Secondary tubules. 2, Tertiary tubules. 3, Interlacing capillaries and air cells.

C. 1, Cavity of tubule. 2, Its lining membrane supporting blood-vessels with large areolæ. 3, Perforations in the membrane at the orifices of the lobular passage. 4, Interlobular space containing the terminal branches of the pulmonary vessels supplying the capillary plexus, 5, to the meshes of which air gets access by the lobular passage.

The lungs occupy only about one-seventh of the thoracic space. They are long, flattened, and oval, extending along each side of the spine from the second dorsal vertebra to the anterior end of the kidneys, and laterally to the juncture of the vertebral with the sternal portions of the ribs. They present two faces, a superior convex and an inferior concave; two borders, an external and an internal; and two extremities, an anterior and a posterior (Fig. 61). The convex surface is also called the dorsal, costal, or superior face. It is moulded on the walls of the thorax and occupies a part of the intercostal space, pushing the intercostal muscles outward. When the surface of the lung is examined it is seen to be furrowed where the ribs pressed during life. These furrows are as deep as the ribs are 197thick. The sides of the lungs are covered with connective tissue which attaches them to the costal walls.

The concave, or inferior, face also called the diaphragmatic or visceral face is directed downward. The diaphragm separates it from the abdominal viscera. The surface is covered by connective tissue which closely attaches it to the diaphragm. It is perforated by the five tubules which bring the posterior air-sac into communication with the lungs.

The borders of the lungs extend parallel to the long axis of the body. The internal border is rectilinear, thick, and rounded. The external border is convex, thin, and sharp.

The anterior extremity terminates in a sharp point which occupies a space formed by the ribs externally and the inferior spines internally. The posterior extremity is somewhat rounded and extends as far back as the anterior border of the kidneys.

As soon as the bronchi enter the lungs they become broadened, the cartilaginous rings disappear, and they continue as membranous channels whose diameters gradually decrease, as they extend backward, to the point where they terminate in the ostium caudale, at which point they are surrounded by a cartilaginous ring. The ostium caudale brings the tubules into communication with the ventral air-sacs.

Twelve air tubules have their origin from each common bronchus, or trunk. Four are given off from the internal wall of the main bronchus by a series of openings arranged in a row. Seven are given off from the external wall by a second series similar to that of the first. The twelfth extends from the inferior wall, and immediately takes a course downward and outward and communicates with the posterior diaphragmatic air-sac. This may be considered as the terminal branch of the trunk.

All of these secondary canals, except the last, pass toward the periphery of the lung. They divide and subdivide at the periphery, covering it with their ramifications. The canals extending from the inner wall are distributed to the inferior face of the lung. Those extending from the outer wall are distributed to the outer face of the lung. The first constitute the diaphragmatic and the second the costal bronchial tubes.

The four diaphragmatic bronchial tubes are numbered in the order in which they are given off. The first is carried forward horizontally, the second transversely inward, the third obliquely inward and backward, 198and the fourth directly backward. They have, by some anatomists, been called the anterior, the internal, and the posterior diaphragmatic bronchial tubes. There are two posterior diaphragmatic bronchial tubes; the larger called the great posterior, and the smaller, which passes directly backward, the small posterior.

The costal bronchial tubes, seven in number, are numbered from the front backward in the order they are given off. Parallel at their origin, and side by side, like pipes of an organ, they soon spread out in fan-shape like the preceding. They extend from their central origin to the periphery. The first extends obliquely upward and inward to the anterior extremity of the lung. All branches from this bronchus extend from its anterior wall. The first branches are inflected to reach the external border of the lung. The succeeding branches are directed forward and the last forward and inward. They all meet those from the anterior diaphragmatic bronchus, but do not anastomose with them.

The second, the third, and the fourth costal bronchi extend in a transverse manner and ramify on the inner border of the lung.

The fifth and the sixth are directed toward the posterior extremity of the lung. The seventh, very small, reaches this extremity, where it disappears.

The first costal bronchus is the largest; those following it gradually become smaller. At their points of origin they adhere closely to the ribs. They are all imperforate, which is a distinguishing feature from those occupying the opposite face.

The canaliculi or tertiary tubules given off by these secondary bronchial tubes do not differ greatly in caliber in the various parts. They are given off at right angles from the pulmonary wall of each bronchus, and extend perpendicularly into the lung substance. Thus we find three kinds of conduits, the primary, the secondary, and the peripheral, or tertiary. The first are like the barbs of a feather on its shaft; and the second and parenchymatous are implanted on the pulmonary walls of the first, like the hairs of a brush on their common base. Thus instead of the branching of the bronchi being dichrotomous, as in mammals, it is piniform.

The canaliculi, or finer tubules, communicate with one another. The inner microscopic appearance of the canaliculi indicate that they are divided into areola, which gives them a cellular aspect. These tertiary bronchi open on a dense labyrinth of blood capillaries 199(Fig. 61, C). At this point the ciliated epithelial cells give way to simple squamous epithelium.

Thus we find three kinds of bronchi, or their ramifications, as follows: the primary, the secondary, and the tertiary.

The Air-sacs (Fig. 61, A).—The air-sacs are bladder-like structures consisting of a delicate cellulo-serous membrane, an extension from the bronchial tubes, in some places strengthened by an external envelope of elastic fibrous tissue. Long thin blood-vessels are distributed in the substance of these walls. They are branches from vessels of the general circulation and not extensions from those of the lungs. No lymphatics have been found in the air-sacs.

Fig. 61, A.—Diagram of air-sacs and their location. 1, The proximal end of the humerus. 2, The proximal end of the right clavicle. 3, The cervical air cell. 4, The right coracoid bone. 5, The anterior thoracic air cell. 6, The right side of the sternum. 7, The right side of the liver. 8, The peritoneum. 9, The right abdominal air cell. 10, The coccyx. 11, The proximal end of the right femur. 12, The right supero-posterior air-sac. 13, The right infero-posterior air-sac. 14, The right lung. 15, The axillary extension of the air-sac. 16, The obturator foramen. 17. The pelvis.

These sacs do not communicate with each other and normally they are not fully inflated. In some locations they extend into the bones and are in communication with the extensions of the bronchial tubes. In fact, by some anatomists they have been called “bladder-like, extra-pulmonary expansions of the bronchial tubes, free from cartilage.” The air-sacs make the bird’s body lighter, thus making 200long-continued flight possible. They are best developed in those birds which fly most. There are four pairs of cells and one single cell from which all other expansions and extensions are made. These sacs are as follows: a single anterior thoracic, and, in pairs, cervical, anterior diaphragmatic, posterior diaphragmatic, and abdominal.

The Anterior Thoracic Air-sac.—The anterior thoracic air-sac is located above the clavicles and the interclavicular space, in the cavity of the thorax. It is related superiorly with the trachea and the esophagus; laterally with the lungs and the cervical air-sacs; inferiorly with the sternum, the clavicle, and the interclavicular aponeurosis; posteriorly with the heart and the anterior diaphragmatic reservoir; and anteriorly with the integuments of the neck. It contains the inferior larynx and the two primary bronchi, and large vascular trunks from which are given off vessels supplying the neck and the wings.

Three prolongations, called subpectoral, subscapular, and middle, or humeral, arise from the lateral walls of this air-sac. These prolongations cross the walls of the thorax and pass around the articulation of the shoulder.

The subpectoral prolongation extends from the thoracic reservoir by an orifice situated behind the coracoid, and passes beneath the tendon of the great pectoral muscle. When the pectoralis major contracts, this contraction dilates the subjacent cell and draws into it a greater quantity of air.

The subscapular and the humeral prolongations communicate with the thoracic air cell by a common opening situated behind the small adductor muscle of the humerus. The subscapular prolongation, after leaving this point, spreads under the scapular and the subscapular muscle, which it separates from the ribs and corresponding intercostal muscles, and extends in a longitudinal direction.

The humeral prolongation, smaller than the subscapular, occupies the axilla, and is in shape triangular. It has from its summit into an infundibular fossa, an extension which enters the canal of the humerus. The walls of this cell form the lining of the air space in the humerus.

The thoracic air-sac thus possesses numerous membranous folds which divide its cavity. The contiguous structures which it overlies, as the trachea, the esophagus, the muscles of the inferior larynx, as well as the arteries and veins, make its outer walls irregular. 201This orifice is dilated during inspiration, by the contraction of the two first fasciculi of the diaphragm.

The Cervical Air-sacs.—The two cervical air-sacs are located just above the thoracic air-sac at the inferior part of the neck and in front of the lungs. They are cone-shaped with the base directed forward and the apex backward. They are related superiorly with the cervical muscles, and inferiorly with the thoracic air-sac from which they are separated by the trachea, the esophagus, the pneumogastric nerve, and the jugular veins. The walls touch each other internally, and form a median septum which includes in its substance the two common carotid arteries. Externally they are related to the origin of the cervical nerves, to each of which they contribute a small sheath. They surround the vertebral artery, and are connected with the subcutaneous muscles and the skin. The summits communicate with the anterior diaphragmatic bronchus. Prolongations extend from their bases which conduct the air into all the vertebræ of the neck and the back, into all the vertebral ribs, and into the spinal canal. Parallel with and adjacent to the vertebral arteries, and lodged in the canals excavated in the transverse processes of the cervical vertebræ, are two cervical prolongations, one on each side, which extend to the cranium from the base of the cervical reservoirs. From their sides, at the last six cervical vertebræ, are six extensions in the form of diverticuli, which, lying against each other, pass from each side into the muscles of the neck. They are surrounded by a thin fibrous envelope, a continuation of the mucous lining of the sac, and apparently form a canal in the inferior part of this region. These prolongations are better developed in palmipedes than in chickens. On the internal side of these prolongations, one or more foramina penetrate the vertebral segment, which allow the extensions of the prolongations into the spinal canal. Chauveau states that “as the medullary tissue is replaced by air in the bones of birds, so is the subarachnoid fluid replaced by air around the spinal cord.”

The prolongations extending from the cervical air-sacs, having entered the thorax, terminate by passing into the first dorsal vertebra. After permeating every part of this vertebra, it escapes by a lateral opening and forms a small sac located between the first two ribs, near the origin of the first dorsal nerve. From this sac an 202extension is given off, which enters the second vertebral segment at the antero-lateral part; from this point it passes back, forming a new air-sac between the second and third ribs. It now passes in the same manner into the third vertebra and extends through the third intercostal sac, and so on till the last dorsal vertebra has been served. At the same time that these sacs receive the air from the vertebræ preceding them, and transmit it to those which follow, they communicate it to all the vertebral ribs. The aerial currents which leave the cervical air-sacs do not communicate with those of the cranium. Experiments show that the cranial bones have apparently no communication with the respiratory apparatus.

The Anterior Diaphragmatic Air-sac.—The two anterior diaphragmatic or supero-posterior air-sacs are related with the lungs anteriorly, and with the abdominal viscera posteriorly. Anteriorly also is the thoracic air-sac, posteriorly are the posterior diaphragmatic air-sacs, and laterally the ribs and the intercostal muscles and internally is the esophagus. The lungs communicate with these air-sacs through circular openings from the great posterior diaphragmatic bronchus and frequently by a second opening from this same tube. These are the only sacs which receive air from the lungs through two openings.

The Posterior Diaphragmatic Air-sac.—The two posterior diaphragmatic, or infero-posterior air-sacs are oval in shape and located between the thoracic and the abdominal cavity. They are related anteriorly with the anterior diaphragmatic air-sacs. These two sacs form a vertical transverse partition. The posterior diaphragmatic air-sacs are related posteriorly with the abdominal air-sacs from which they are separated by the diaphragm. They are related below with the lateral parts of the sternum and the sternal ribs, and externally with the ribs and the intercostal muscles. These air-sacs communicate with the lungs through openings located in the middle part of the external border of the lung, into the extremity of voluminous bronchial tubes which follow the direction of the largest air tubes.

The Abdominal Air-sacs.—The two abdominal air-sacs located on each side of the abdominal cavity, when inflated with air, form enormous bladder-like structures. They are related laterally with the abdominal wall and internally with the abdominal viscera. The anterior extremities are in communication with the mesobronchi and are somewhat inflected to pass under the fibrous arches extending 203from the spine to the pelvis. Anteriorly these sacs adjoin the diaphragm, the testes in the male, and ovary in the female, and to the parietes of the abdomen and those of the pelvis. Below and in front, they rest on a fibrous septum, which in all birds divides the abdominal cavity into two smaller cavities: one anterior, representing the abdomen and containing the liver; the other posterior, representing the pelvis and containing the gizzard and the intestines. The anterior portion overlies the posterior part of the lobes of the liver, the proventriculus, the spleen, and the gizzard. The kidneys are located above these air-sacs. Dorsal to the sacs is also a part of the intestines and in the female the oviduct. The abdominal air-sacs are attached by a ligament-like structure in their medial, their anterior, and their lateral margin. The posterior, the dorsal, and the ventral margin are free. Mesially this attachment is to the mesentery, connecting the left cæcum to the dorsal margin of the gizzard, and also to the mesentery of the proventriculus. The anterior attachment is to the body wall and extends in front of the end of the ovary and the adrenal glands. At the antero-lateral part of the body cavity the attachment extends in a widening band along the lateral side of the ovary and of the oviduct, as far back as the caudal margin of the sac. The lateral attachment is related to the kidney, the dorsal ligament of the oviduct, and the abdominal wall.

Each of these abdominal sacs has three extensions: one suprarenal and two femoral.

The suprarenal extension leaves the principal sac at the postero-external part of the kidney, extends upward, and forward, and expands over the surface of the kidney. At the internal border of the kidney, this prolongation extends between the transverse processes of the sacral vertebræ, reaches a height of the first dorsal vertebra, forms a triangular canal located above the sacrum in the sacral channel, and is separated from its fellow by a series of corresponding spinous processes.

The two femoral extensions, an anterior, small, and a posterior, large, extend from the abdominal air-sac at the cotyloid cavity, leave the pelvis through the bony passage occupied by the crural vessels, extend around the coxo-femoral articulation, and terminate in a blind extremity. In some birds, particularly in birds of prey and ostriches, there are prolongations extending into the femur, entering through a foramen at the anterior part of the great trochanter.

204Summary of Bones Supplied by Each Air-sac.—The thoracic air-sac communicates on each side of the thorax with twelve bones, including the four sternal ribs. It supplies air to the clavicles, which are perforated at both their extremities, and to the coracoids, which are perforated just below their scapular extremity. The sternum is supplied through two series of openings, the middle ones that conduct air into the sternal ridge and the lateral ones, eight in number and very small, correspond to the intercostal spaces. The sternal ribs are penetrated by small foramina at their inferior extremities. From the subscapular extension the scapulæ receive air through one or two foramina at their anterior extremity. The humeral prolongation supplies the humerus through a foramen located at the upper edge of the humeral fossa, at the infero-internal part of the articular head.

The cervical air-sac furnishes air to all the cervical vertebræ, to all the dorsal vertebræ, and to all the vertebral ribs. The anterior parts of the vertebræ of the neck are supplied with air through the passage accommodating the vertebral artery. The posterior parts of the vertebræ are supplied by extensions from the interspinal canal. The first extensions obtain entrance to the anterior segments by one or more openings of the inner wall of the intertransverse canals; the median extensions penetrate the posterior segments by two openings, a right and a left, situated on the inner wall of those segments. The first dorsal vertebra is supplied with air in the same manner, by the middle and the lateral canals of the neck. This air, after passing through the first vertebra, leaves by a lateral exit to enter a small air-sac. From this it passes into the superior part of the second vertebra, escapes from this through its lower portion, to be received into a lateral sac, and so on to the last dorsal vertebra. These sacs also supply the vertebral ribs with air, which enters them by very small openings located on their spinal extremities.

The diaphragmatic air-sacs do not have communications with the bones.

The abdominal air-sacs communicate with the sacrum, the coccygeal vertebræ, the iliac bones, and the femurs. The air passing through the sacrum, the coccyx, and the ilium comes directly from the suprarenal extensions; the air which fills the femoral cavity comes from the femoral extensions.

In some birds these air spaces are more greatly developed than in 205others. The bones that are always aerated in all birds are the cervical and the dorsal vertebræ, the sternum, and the humeri. Those aerated in some kinds only are the furculum, the scapulæ, the vertebral and the sternal ribs, the sacrum, the coccyx, and the femurs. Those that are never aerated are the bones of the forearm, the hand, the leg, and the foot.

The service of air to the bones in most parts of the body by the air-sacs, as just shown, is in special cases otherwise rendered. The Eustachian tubes furnish air to the bones of the cranium and to the upper jaw; while the lower jaw receives air from the pneumatic foramen situated upon each ramus behind the tympanic articulation, and from an air cell which surrounds the joint.

The cavities of the embryonic bones, which afterward become pneumatic, are filled with marrow. Selenka states that the invasion of the bones by the air is a late development, and that in the humerus this invasion occurs after the twenty-second day in the life of the chick.

Hunter and Compar, who have made extensive researches, consider the function of the air-sacs as threefold.

First, the air-sacs are subsidiary respiratory organs, which aid in ridding the blood of waste products and in taking in oxygen.

Second, they aid mechanically the actions of respiration in birds. During the act of inspiration the sternum is depressed, the angle between the vertebral and the sternal ribs is made less acute, and the thoracic cavity proportionately enlarged; the air then rushes into the lungs and into the thoracic receptacles, while those of the abdomen become flaccid. When the sternum is raised, or approximated toward the spine, part of the air is expelled from the lungs and the thoracic air-sac through the trachea, and part is driven into the abdominal receptacles, which are thus alternately enlarged and diminished with the expansion and the contraction of the thorax. Hence the lungs, notwithstanding their fixed condition, are subject to due compression through the medium of the contiguous air receptacles, and are affected equally and regularly by every motion of the sternum and of the ribs.

Third, they reduce decidedly the specific gravity of the whole body. This must necessarily follow from the large spaces filled with air as well as from the absence in the bones of marrow and other fluids. The air-sacs by their position also render equilibrium more stable.

ANGIOLOGY — THE HEART (Fig. 21, No. 7) — THE BLOOD-VESSELS — The Arterial Trunks — Branches of the Carotid Trunk — Branches of the Carotis Cerebralis — Branches of the External Carotid Artery — Branches of the Vertebral Artery — Branches of the Subclavian Artery — Branches of the Brachialis Profunda — The Venous Trunks — THE VEINS OF THE HEAD — Branches of the Vena Facialis Interna — Branches of the External Facial Vein — Branches of the Vena Cephalica Posterior — BRANCHES OF THE VENA OCCIPITALIS EXTERNUS — THE VENOUS SINUSES OF THE HEAD — VEINS OF THE BRAIN CAVITY — THE VEINS OF THE NECK — Branches of the Vena Jugularis — THE VEINS OF THE DORSAL REGION — VEINS OF THE THORAX — Branches of the Vena Subclavia — VEINS OF THE FORE LIMB — THE POSTERIOR VENA CAVA — THE VEINS OF THE POSTERIOR EXTREMITY — VEINS OF THE CAUDAL REGION AND OF THE PELVIC CAVITY — VEINS OF THE TRUNCUS VENA ILIACA COMMUNIS — VISCERAL VEINS OF THE POSTERIOR VENA CAVA — The Lymphatic System — The Blood and Its Functions — THE FATE OF THE ERYTHROCYTE OF THE FOWL

The Circulatory Apparatus.—The circulatory apparatus consists of two tubular systems: the blood vascular system and the lymphatic system.

The blood vascular system consists of the heart, the arteries, the veins, and the capillaries.

The heart is the central, propelling organ. The arteries form a series of efferent tubules, which, by branching, constantly increase in number and decrease in caliber, and which serve to carry the blood from the heart to the tissues. The capillaries are extensions from these latter tubules into which the arteries empty, and through the walls of which the interchange of elements between the blood and the other tissues takes place. The veins form a system of converging tubules which receive the blood from the capillaries, decrease in number and increase in size as they approach the heart, and return the blood to that organ.

The lymphatic system consists of capillaries and veins alone. As in the blood system, the lymph capillaries collect the effete material and pour it into the lymph veins, and these in turn, carry it to the large blood veins adjacent to the heart.

Both these systems have one and the same continuous lining, which consists of a single layer of endothelial cells. In the heart this lining is called the endocardium, and in the vessels, the endothelium. It forms a perfectly smooth surface.

The heart of the domestic fowl is located in the median line of the thoracic cavity. It is more anterior and mesial than in mammals. Its axis is parallel with the axis of the trunk. The lungs being confined to the dorsal part of the trunk, the lower part of the heart is not surrounded by them, but extends backward, the apex resting in the anterior part of the anterior median fissure of the liver.

The heart has the form of an acute cone (Fig. 50, No. 1), the apex of which is bluntly rounded.

207The heart is surrounded by a sero-fibrous sac, the pericardium. This sac adheres to the cervical air reservoirs anteriorly and to the diaphragmatic septum posteriorly. It is composed of two membranous layers: the parietal, external, dense, and fibrous; and the visceral, internal, and serous. The pericardial sac has no direct attachment to the heart, except at the upper extremity where it surrounds the large vessels emerging from it. The serous layer is reflected over the outer portion of the heart, where it is called the epicardium. The function of the pericardium is to prevent friction during the beating of the heart. It contains a small amount of serous fluid for perfect lubrication. This fluid is called the liquor pericardii.

Internally the heart has four cavities: two auricles and two ventricles. The right ventricle is more crescent-shaped than in solipedes, and in a manner envelops the left ventricle in front and to the right, though it does not reach the point of the heart. The right auricle is larger than the left. The auriculo-ventricular valve is not tricuspid as in mammals. This valve instead of being formed as usual by a membranous curtain, with margins retained by cords fixed to the walls of the ventricles, is composed of a wide muscular leaf, which appears to be a portion of the inner wall of the ventricle detached from the interventricular septum. This septum is convex; and the auriculo-ventricular orifice is an oblique slit situated between it and the muscular valve in question; so that, when the heart wall contracts at the systole, the valve is applied against this septum and closes the passage. The bicuspid, or auriculo-ventricular valve of the left side usually has two segments, though occasionally there may be three. The fossa ovalis is a depression behind the posterior semi-lunar valve in the septum of the heart. The membranous septum closing the foramen ovale is complete and strong but thin and transparent. The right auricle receives the blood from the two venæ cavæ coming from the anterior extremity, and from the posterior vena cava. These empty into a sinus. The left auricle has two vessels, the pulmonary veins which bring blood to it from the lungs.

Structure of the Heart.—The heart is lined by a serous membrane, the endocardium, which is a continuation of the endothelium of the blood-vessels. There are a few muscular pillars in the inner wall, called the columnæ carnæ. To give the heart its pumping power, it is made up of contractile tissue, a specialized kind of muscle 208called heart muscle. It is involuntary-striated and occupies an intermediate position, both morphologically and embryologically, between smooth involuntary muscle and striated voluntary muscle (Fig. 74, No. 4). It, like striated voluntary muscle, is both transversely and longitudinally striated. Heart muscle cells are short, thick cylinders, which are joined end to end to form long fibers. By means of lateral branches the cells of one fiber anastomoses with cells of adjacent fibers. Each cell of heart muscle contains one centrally located nucleus. There is no distinct sarcolemma, but the sarcoplasm is more dense near the surface of the cell, which gives it the appearance of an enveloping cell wall. There is a zone free from fibrillæ around the nucleus. The longitudinal fibrillæ, which make up the cell, are held together by a cement-like substance.

The main mass of the heart wall, called myocardium, consists of the specialized muscular tissue just described. The myocardium differs in thickness in different parts of the heart wall. It is thickest in the left ventricle and thinnest in the auricles. The left ventricle forces the blood through the systemic circulation and hence must be thicker to give it more power than is needed for the right ventricle, which forces the blood only through the lungs. The auricles are thinnest of all; for they receive the blood and pass it only to the chambers below. The auricular appendages at the base of the heart in fowls are not so well marked as in mammals. The auricular muscles consist of an outer coat common to both auricles, the fibers of which are transverse and of an inner coat, independent for each auricle, the fibers of which are longitudinal. Between the two coats, occur bundles of muscle the fibers of which run in various directions. The disposition of the muscle tissue of the ventricles is much more complicated. It is composed of several layers of fibers intricately interwoven.

The endocardium, covering the inner surface of the myocardium, forms a serous lining of all the chambers of the heart. At the arterial and venous openings it is continuous with and similar in structure to the intima of the vessels. The endocardium consists of two layers, an external layer closely attached to the myocardium and consisting of mixed fibers, including those of elastic tissue and smooth muscle cells; and an inner, single layer of endothelial cells, spoken of above.

The heart is supplied with nutrient blood by the two coronary 209arteries, which are given off from the common aorta just above the semi-lunar valves.

A right, or anterior, and a left, or posterior, coronary from their point of origin, turn in a ventral direction between the root of the aorta and the pulmonary artery, the right going to the right coronary groove and the left to the left coronary groove in the crown furrow. From here they send branches into the heart. The anterior, right, coronary, or coronaria dextra, the larger, is given off from the inferior wall of the aorta. It divides into a ramus superficialis and a ramus profundus. The ramus superficialis enters the crown furrow and divides into two or three branches on the right heart wall. These branches extend to the apex of the heart. Twigs from this artery along its course extend into the muscular wall reaching the posterior of the coronary groove where they anastomose with those of the left coronary, the ramus profundus, and with other branches from the same artery. The ramus profundus, larger than the preceding, gives off fine branches into the walls of the aorta and of the pulmonary artery, then enters from behind into the right wall of the septum ventriculorum, extends into the apex of the heart, and supplies the septum, or right inner chamber wall with the last branch, this breaking through the posterior wall of the auricular appendage.

The posterior, left coronary, or coronaria sinistra, originates from the dorsal wall of the aorta, proceeds as one branch on the upper surface of the left auricular appendix, and then extends between the left appendix and the pulmonary artery to the ventral surface of the heart. On the left side it supplies the wall of the pulmonary artery and gives off a ramus profundus. It sometimes divides into two parts and supplies the ventral wall of the right chamber and then extends to the left wall of the septum medium. The rest of the coronaria sinistra enters into the left crown furrow as the ramus superficialis, which provides the left and dorsal upper surface of the left chamber to the apex. From this furrow it extends into the left chamber and the left appendage, and finally fuses with the ramus superficialis of the coronaria dextra.

The blood-vessels consist of arteries, veins and capillaries.

The Structure of the Capillaries and Arteries.—The capillaries are minute vessels which connect the arterioles, or terminal arteries, 210with the venules, or terminal veins. They are only from 6 to 14 microns in diameter. Their walls consist of a single layer of endothelial cells, which are somewhat elongated in the long axis of the vessels. Their edges are serrated, and are united by a small amount of intercellular cement-like substance. Capillaries branch without diminution in caliber, and these branches anastomose to form capillary networks, the meshes of which differ in size and shape in different tissues and organs. The largest meshed networks occur in the serous membranes and in the muscles; and the smallest occur in the glands, such as the liver.

The walls of the arteries are thick and stand open when empty, owing to the elastic tissue contained in their walls, while the walls of the veins collapse when empty, owing to their containing a smaller amount of elastic tissue. The arterial wall is provided with three coats: tunica intima, or inner coat; tunica media, or median coat; and tunica adventitia, or outer coat.

The tunica intima consists of a single layer of endothelial cells, continuous with and similar to that forming the walls of the capillaries. In passing from the capillaries to the arterioles, there is first a thin coat, or sheath-like layer, of connective tissue around the outside of the endothelial tubes. Further along, isolated smooth muscle cells arranged in a circular manner occur between the endothelial layer and the layer of connective tissue, this structure forming vessels called precapillary arteries. Further along still, the muscle cells form a complete layer; in this section the vessels are called arterioles and are made up of three coats: the inner endothelial, the middle muscular, and the outer fibrous.

In arteries of medium size the intima consists of the endothelial layer, a layer of delicate white and elastic fibers, connective-tissue cells, and the membrana elastica interna, or an outer layer, the elastic layer, of the intima.

The media consists of a thick coat of circularly arranged smooth muscle cells, its thickness depending largely upon the size of the vessels. There is also a small amount of fibrillary connective tissue, which supports the muscle cells. Elastic tissue is present in the media, the amount depending on the size of the vessel, the larger the vessel the more elastic tissue there is present. In the large arteries coarse elastic fibers intermingle with the finer ones. When much elastic tissue is present the muscle cells are separated into more or less well-defined groups.

211The adventitia is composed of loose connective tissue with some elastic fibers. A few smooth muscle cells are present, which, as are also the elastic fibers, are arranged longitudinally. The adventitia, blending with the connective tissue surrounding the arteries, serves to anchor the vessels to the surrounding structure.

Structure of the Veins.—In many respects the walls of the veins resemble those of the arteries. The same three coats exist and the same elements enter into their structure. The transition from capillary to small veins, and from those to larger veins, is similar to the transition from the arteries to capillaries, in inverse order. The walls are not so thick as those of arteries. The elastic tissue is much less in quantity and in smaller veins disappears. There is not a clear line of demarcation between the intima and the media.

The veins of birds differ from those of mammals in that they have fewer valves. The valves are also less perfect, and often permit a backward flow of blood.

The walls of the arteries and of the veins are supplied with nutrient blood-vessels. These are called the vasa vasorum, or blood-vessels of the blood-vessel wall. They are mostly in the adventitia. They may arise from the vessel to which they are distributed or take origin from an adjacent vessel. These small arteries supplying the vessel coat after terminating into capillaries form small veins through which the blood, from the structure of the vessel wall, is returned.

The walls of the blood-vessels are supplied with both medullated and non-medullated nerves. The non-medullated nerve fibers are axones of the sympathetic neurones and control the caliber of the vessels. These fibers are called the vasomotor nerves. They form plexuses in the adventitia, from which are given off branches which penetrate the media and terminate on the muscle cells. The medullated nerves are the axones of the spinal nerves. The larger fibers are found in the connective tissue outside the adventitia and give off branches to the media where they divide repeatedly, lose their sheath, and terminate in the media and at times in the intima.

The common aorta is short; it originates from the left ventricle (Fig. 61B, No. K, 14), and is guarded by three semi-lunar valves. The aorta breaks through the pericardium just to the right of the pulmonary arteries in a ventral direction; it then turns upward dorsally and to the right of the inferior bodies of the vertebræ. It is then 212directed anteriorly, and dorsally to the right bronchus, between the right bronchus and the right lung. The right and the left coronaries are given off from the common aorta; they have been discussed. There is next given off the left brachio-cephalic or brachio-cephalic sinister artery (Fig. 61B, No. K, 10), which is just above the border of the base of the heart. This artery passes upward and slightly forward, over the center of the inferior larynx. Just beyond this point the subclavian artery is given off; this artery later becomes the axillary and the axillary the brachial artery. Then there is given off the anterior and the posterior thoracic arteries; and finally, the pectoral, which supply the pectoralis muscles and later terminate in the carotid, the vertebral, and the cervical arteries. The carotid artery gives off an esophageal artery. The other arterial trunk given off from the common aorta is the right brachio-cephalic or brachio-cephalic dexter (Fig. 61B, No. K, 18). The right brachio-cephalic artery gives off the subclavian, which continues as the axillary, and continues as the brachial artery. There is given off the anterior and the posterior thoracic, the right carotid (Fig. 61B, No. K, 11), the vertebral, and the dorsal. The last continues as the cervical.

Fig. 61B.

K. The arterial trunks. 1, The middle sacral artery. 2, The hypogastric
artery. 3, The posterior mesenteric artery. 4, The ischiadic artery. 5, The
femoral artery. 6, The renal artery. 7, The left pectoral artery or thoracico
caudalis. 8, The left axillary artery. 9, The left carotid artery. 10, The left
brachio-cephalic artery. 11, The right carotid artery. 12, The right brachial
artery. 13, The right pectoral artery. 14, The common carotid artery. 15,
The posterior aorta. 16, The celiac axis. 17, The anterior mesenteric artery.
18, The right brachio-cephalic artery. 19, The auricular portion of the heart.
20, The ventricular portion of same. 21, Sterno-clavicular artery. 22, Anterior
thoracic.

L. The venous trunks. 1, The caudal vein. 2, The coccygeo-mesenteric vein. 3, The posterior mesenteric vein. 4, The anterior mesenteric vein. 5, The gastro-duodenal vein. 6, The portal vein. 7, The hepatic vein. 8, The left anterior vena cava. 9, The left pectoral vein. 10, The left brachial vein. 11, The left jugular vein. 12, The right jugular vein. 13, The right brachial vein. 14, The right pectoral vein. 15, The right anterior vena cava. 16, The posterior vena cava. 17, The common iliac vein. 18, The femoral vein. 19, The renal vein. 20, The internal iliac vein. 21, The hypogastric vein. 22, The auricular portion of the heart. 23, The ventricular portion of same.

213The pulmonary arterial trunk is given off from the conus arteriosus of the right ventricle. It is guarded at its origin by three semi-lunar valves similar to those of the aorta. The trunk divides into two pulmonary arteries, which are short, one called the pulmonalis dexter and the other the pulmonalis sinister. The former goes to the right and the latter to the left lung. Each branch penetrates the lung near the bronchus. These arteries divide, or branch, similarly to the bronchi. Following the branchings of the bronchi, they finally terminate into the lung capillaries, forming networks on the bronchi and the air-tube terminals.

214The cord-like remnant of the ductus botalli, or embryonal connection between the lung arterial trunk and the anterior aorta, has been observed but is rare in grown birds.

The arteries, the veins, and the lymphatic vessels of birds anastomose far more frequently than those of mammals.

The carotis communis artery springs from the carotid trunk of the brachio-cephalic. It is directed horizontally, ascending to the ventral side of the neck. It then extends downward to the inferior median neck region. Just after leaving its origin it gives off several small branches to the bronchi and to the esophagus, and extends toward the head. The carotid lies on the thyroid gland and at this point touches the jugular vein (Fig. 21). At this point the thyroid arteries are given off from the carotid trunk. The thyroid gland also receives blood from the bronchialis artery.

Dorsalward and near the thyroid gland the carotid artery gives off a branch (the bronchialis) which accompanies the recurrent laryngeal nerve, along the inferior larynx and the bronchi, and supplies the lung substance and that part of the esophagus in this region.

The vertebral artery is given off from the carotid trunk, dorsalward to the thyroid gland, and on the left side. The right vertebral artery may be given off from the brachialis dextra or right brachialis.

The inferior esophageal artery is given off from the ventral side of the carotid, supplies the esophagus, extends then to the skin of the neck and to the trachea, is directed anteriorly toward the head and anastomoses with the vertebral artery. This artery accompanies the vagus nerve and forms a collateral artery to the carotid and the vertebral artery.

The subcutaneous colli springs from the carotid artery near the thyroid gland and communicates with the inferior cervical artery, which, in turn springs from the vertebral artery.

The Common Carotid.—Near the last cervical vertebra the two carotid arteries occupy the same channel, to which they are attached by fascia, and, lying close to the inferior surface of the bodies of the cervical vertebræ, are covered by the colli muscles. Near the third or the fourth cervical vertebra, the two carotid arteries separate. Near the atlas each carotid divides into the carotis cerebralis and carotis externa. Near this division the superior cervical artery branches off. This latter artery extends down the neck in company with the pneumogastric nerve and the jugular vein, supplies the skin and the neck muscles, and anastomoses with the inferior cervical artery and the subcutaneous colli artery.

216The occipital artery originates either from the carotis communis or sometimes from the superior cervical.

The branches of the carotis cerebralis are as follows:

1. The occipitalis (Fig. 72, No. 18), which in turn gives off, first, the occipitalis sublimis. The occipitalis sublimis supplies the outer and the middle portion of the digastricus and the posterior mylo-hyoideus muscle. It also gives off, second, the occipitalis profunda which supplies the inner portion of the digastricus muscle and becomes the meningeal artery, which passes through the foramen vagi, entering the brain cavity, where it supplies the coverings of the brain as far as the sella turcica. Superficial branches of this artery are distributed to the muscles in the region of the atlas and anastomose with the vertebral artery.

2. The ophthalmica externa, which passes below the articulation of the quadrate bone, around the tympanic cavity, enters the canalis caroticus, and passes into the cranial cavity. The ramus occipitalis, passing out of the same foramen, again enters the diploë of the cranium; then after passing dorsally over the upper outer semicircular canal of the ear, passes backward through the occipital bone.

The ophthalmica externa (Fig. 72, No. 9) forms a main trunk and gives off two branches: the temporal artery and the recurrent ophthalmic. The recurrent ophthalmic gives off the rete temporalis, rete ethmoidalis, a branch to the orbital gland, and finally anastomoses with its own branches and with those of the internal ophthalmic at the olfactory foramen and aids in forming the ethmoidal artery. These arteries supply blood by giving off branches to the muscles of the eye, sclerotic coat, iris, choroid coat, and the ciliary bodies. It gives off another branch to Harder’s gland, and finally anastomoses with the ethmoidalis.

3. The plexus temporalis, rete mirabile ophthalmicum, or wonderful network (Fig. 72, No. 8), is formed between the second and the third trunk of the trigeminus nerve and the rete ophthalmicum.

Inferior to this is the alveolar plexus, which plexus accompanies the third branch of the trigeminus into the lower jaw. Two main branches form this plexus, one coming from the carotis facialis, which anastomoses with the alveolar artery.

217The palpebral plexus lies between the trunks of the trigeminus, and supplies mainly the lower eyelid.

The plexus muscularis extends to the fifth portion of the temporal muscle.

The plexus lacrimalis forms on the posterior orbital wall on the ramus ethmoidalis and supplies the lacrimal gland and the upper eyelid. It anastomoses with branches from the facial artery.

The ramus ciliaris posticus supplies the inferior rectus and the external rectus muscle of the eyeball. It anastomoses with the ophthalmica externa.

The median meningeal artery passes through the foramen occupied by the second branch of the trigeminal nerve. Passing into the cranial cavity, it supplies the dura mater. Before passing into this foramen, small branches are given off, which supply the skin and the temporal muscle; and some branches anastomose with the superior cervical and the ethmoidal arteries.

4. The Cerebral Artery.—Each cerebral artery enters the cranial cavity through the canalis caroticus located in the sphenoid bone, passes forward medially from the cochlea, dorsally from the Eustachian tube, and passes through a small canal which opens on the inner surface of the sella turcica. Originating in this foramen, the sphenoid artery divides into two branches which anastomose with the pterygoidean and the pterygo-pharyngeal artery and which supply the upper jaw and the throat regions.

The spheno-maxillaris artery supplies the gums.

The right and the left cerebral arteries unite at the sella turcica. After this union they divide again immediately and pass to the base of the brain, where they give off twigs to the optic nerve, to the optic chiasm, and where also is given off the arteria retinæ centralis. Passing posteriorly each cerebral artery gives off the ramus posterior, and then passes to the side of the cerebellum.

The basilar artery, a continuation of the anterior spinal artery, is located ventrally and mesially to the cerebellum. Laterally and inferiorly the basilar artery gives off the inferior cerebellar artery.

The ramus anterior is given off from the cerebralis artery and continues as the internal ophthalmic artery. The ramus anterior also gives off the sylvian artery, which supplies the sides of the cerebrum and the middle brain. In the fissure between the hemispheres and the optic thalamus is located the arteria cerebri profunda. This artery passes along the median surface of the cerebrum and in 218its course supplies the adjacent parts. It enters into the formation of the choroid plexus of the lateral ventricle.

The internal ophthalmic artery extends out of the cranial cavity, through the optic foramen, into the orbital cavity. It passes upward along the interorbital wall and supplies the optic nerve, the trigeminus nerve trunk, and the eye muscles, and dorsally anastomoses near the olfactory nerve with the rete ethmoidale and the external ophthalmic artery, and continues as the ethmoidal artery.

The ethmoidal artery supplies the supra-orbital gland and the gland of Harder. It gives off twigs to the rete ophthalmicum and other branches to the skin of the frontal region, where it anastomoses with branches of the external facial artery. These branches in the frontal region are rather large. Large branches are given off to the comb.

The arteria ethmoidalis externa originates in the nasal cavity from a division of the ethmoidal artery.

The external ethmoidal artery passes below the lacrimal bone, extends forward, supplies the walls of the nasal cavity, and finally sends a branch anteriorly into the upper median portion of the jaw bone, and other branches to the septum nasi and other parts of the nasal cavity.

There are frequent anastomoses between the ethmoidalis interna, the facialis, and the spheno-maxillary artery.

The internal ethmoidal artery supplies principally the posterior turbinated bones and septum nasi.

Branches from the external carotid and the facial artery supply the tongue and its muscles, the larynx, the lower jaw bone, the gums, and the upper lateral facial region.

The external carotid (Fig. 62, No. A, 8) gives off the following branches:

First, the hyoid artery (Fig. 72, No. 12) which supplies the inner portion of the depressor mandibular and also the cornua of the os hyoideum, and extends to the tip of the tongue.

Second, the superior laryngeal artery (Fig. 72, No. 16) which supplies the sterno-brachialis and gives off branches which extend downward to the trachea and to the esophagus. The main artery passes along the left side of the esophagus and anastomoses with branches of the inferior esophageal, forming collateral circulation in that region.

219

Fig. 62.

A. Blood-vessels of the head. 1, The cerebellum. 2. The cerebrum. 3, The semicircular canals. 4, Sinus occipitalis superior. 5, Sinus temporalis sphenoideus. 6, Sinus transversus dexter. 7, Superior esophageal artery. 8, Carotis externus. 9, Lingual artery. 10, Sinus longitudinalis.

B. Veins of the antero-inferior part of the head and neck. 1, The right carotid artery. 2, The left carotid artery. 3, Vena jugularis dexter. 4, Vena vertebralis dexter. 5, Transverse vein. 6, Vena cephalica dexter anterior. 7, Vena lingualis. 8, Vena cephalica posterior. 9, Vena facialis externa dexter. 10, Vena infrapalatina. 11, Posterior nares. 12, Vena facialis interna. 13, Vena facialis externa sinister.

C. The brain. 1, Medulla oblongata. 2, Cerebellum. 3, Optic lobe. 4, Cerebrum. 5, Longitudinal fissure. 6, Transverse fissure. 7, Olfactory nerve. 8, Optic nerve. 9, Optic commissure. 10, Motor oculi. 11, Patheticus. 12, Trigeminal, or trifacialis. 13, Abducens. 14, Facialis. 15, Auditory, or acousticus. 16, Glosso-pharyngeus. 17, Pneumogastric. 18, Spinal accessory. 19, Hypoglossus. 20, Hypophysis. 21, Crus cerebri. 22, Ganglion on superior nerve trunk. 23, Spinal cord. 24, A pair of spinal nerves.

220Third, the lingualis artery (Fig. 62, No. A, 9) which lies between the mylo-hyoideus and the posterior part of the hyoid bone. It supplies the tongue muscles. It passes to the median surface of the lower jaw bone, where are given off small branches which enter the jaw and anastomose with the inferior alveolar artery.

Fourth, the Facial Artery.—The facial artery divides into the following branches:

The auricular artery is given off near the articulation of the os quadratum with the os zygomaticum. It is located at the outer auditory canal, and its branches are distributed to the parotid region and to the depressor mandibular, or digastricus, muscle.

The external facial artery is located between the os quadratum and the masseter muscle. It gives off a branch to the lower jaw bone and to the skin of that region, and then passes to the lacrimal bone and supplies branches to the commissure of the mouth, the auditory canal, the masseter muscle, the three eyelids (upper and lower eyelids and the membrana nictitans), the nose cavity, and the skin in the frontal region. It communicates on the other side with the ethmoidal artery.

The internal facial artery passes over and through the os pterygoideum, supplies all the jaw muscles, and is continued as the inferior alveolar artery.

The inferior alveolar artery enters the canal of the lower jaw bone along with the mandibular nerve. It is finally continued as the mental artery, leaving the canal, and passing to the outer jaw surface.

The facialis continues as the internal maxillary artery.

The internal maxillary artery (Fig. 72, No. 15) supplies the pterygoid muscle, the upper part of the pharynx, the commissure of the mouth, the salivary gland region, the gums, and finally anastomoses with branches of the spheno-maxillaris artery.

The vertebral artery is given off, dorsally near the thyroid gland, from the carotis communis or from the carotid trunk. The vertebral artery passes horizontally and dorsally into the canals formed in the transverse processes of the cervical vertebræ. After it leaves the carotid, it is divided into anterior and posterior branches.

221The posterior vertebral artery passes in the canals of the transverse processes of the fifth or sixth dorsal vertebra. It sends branches into the vertebræ, into the spinal canal, and into the intercostal muscles between the ribs and anastomoses with the intercostal arteries.

The anterior vertebral artery is larger than the posterior. It extends laterally along the side of the neck in the foramen of the transverse processes of the cervical vertebræ, and lies along the course of the inferior vertebral vein and the deep imbedded trunk of the sympathetic nerve. It continues to the head. In its passage it gives off to each vertebral segment a dorsal and a ventral branch. Twigs from these branches pass into the bodies of the vertebræ and the spinal canal, giving nutriment to the bony structure and to the spinal cord and its coverings. Other twigs are distributed to the muscles of the neck and some finally anastomose with branches of the carotis communis. This artery, reaching the head, gives off a long anastomosing branch which passes between the atlas and posterior part of the occipital bone and joins the ramus profundus and the occipital artery, thus again communicating with the carotid artery. The remainder of the vertebral artery is small and passes through the foramen magnum into the cranial cavity where it anastomoses with terminal branches of the cerebral artery. At the base of the neck and before the vertebral artery enters the canal of the cervical vertebræ, it gives off the arteria cervicalis ascendens, superior artery of the crop (Fig. 73, No. 18) which branches out on the upper surface of the crop is also distributed to the neck muscles, and later subdivides into the transverse cervical arteries which supply the skin and the muscles of the base of the neck, and the shoulder region.

On the ventral side of the neck there are given off two subvertebral carotid arterial branches. They lie in a shallow furrow on the ventral side of the cervical vertebræ and close to the median line.

The subclavian artery (Fig. 20, No. 13; Fig. 73, No. 11) gives off the following branches:

1. Sterno-clavicularis (Fig. 73, No. 9) which originates on the upper part of the subclavia, between the carotid artery and external thoracic (Fig. 73, No. 3), divides into many branches. The sterno-clavicularis 222gives off the sternal artery, which enters by the side of the supra-coracoid muscle and the anterior rim of the sternum. It is distributed to the inner surface and over the air-sac. Another outside branch passes the posterior end of the crista sterna and supplies the large breast muscles.

The clavicular artery (Fig. 73, No. 8) accompanies the clavicle to the shoulder-joint.

The acromial artery is given off from the sterno-clavicularis on the ligament near the shoulder-joint.

2. The thoracic artery branches from the subclavian artery (Fig. 70, No. 4). The thoracic artery gives off the following branches:

The internal mammary, or internal thoracic artery (Fig. 73, No. 16) arises on the inner side of the sternum and extends downward and backward, giving nutrient branches to the anterior vena cava and to the diaphragm. At the point of the costo-sternal muscle it divides into an inner and an outer branch.

The inner branch supplies the costo-sternal muscle and extends along the ribs and along their juncture with the breast-bone. It finally extends posteriorly, giving numerous branches to the abdominal muscles. The outer branch is distributed in a similar manner, giving off branches to the diaphragm and to the abdominal muscles, and anastomoses, on the surface of the abdominal muscles, with the epigastric artery.

The external thoracic artery (Fig. 73, No. 3), ramus superior, supplies principally the large breast muscles.

The inferior thoracic artery, external ramus inferior, passes along the outside of the pectoralis major muscle, extends downward, and gives off the arteria thoracica longa (subcutaneous thoracic). This latter artery supplies the skin of the breast region. Other branches are given off to the muscles of the breast and to the skin of the region, and some finally anastomose with the branches of the sternal artery.

3. The axillary artery (Fig. 73, No. 12) extends out of the thoracic cavity along with the brachial nerve plexus. It gives off the subscapularis which supplies the muscles of the scapular region. The axillary artery terminates as the brachialis which passes between the biceps brachii and anconeus muscles downward along the humeral shaft. It gives off the anterior humeral circumflex artery and the brachialis profunda artery (Fig. 68, No. 3). It gives off near the elbow-joint the ulnar and radial arteries.

223The anterior circumflex humeral artery passes through the short head of the biceps and gives off a branch to the biceps muscle, supplying the insertional part of the breast muscles.

The brachialis profunda artery (Fig. 68, No. 3) continues as the posterior circumflex humeral artery. This artery supplies the muscles of the posterior part of the humerus, the skin of the wing, and the muscles of the brachial region. The trunk of the arteria brachii profunda passes downward along the anconeus muscle, supplying that muscle and giving off the collateral ulnar artery. On the ulnar olecranon it anastomoses with the recurrent ulnar, thus establishing, at this region, collateral circulation. The rest of the brachialis sends branches to the biceps muscle and to the skin of the upper arm, and finally gives off the arteria collateralis radialis, which supplies the condylo-ulnaris. It then anastomoses with the end branches of the recurrent radialis artery.

The radial artery (Fig. 67, No. 4) passes downward on the outer rim of the forearm. It continues down to the carpal region, where it supplies the muscles and the skin of the carpal region it gives off the recurrent radial, which passes on the middle finger and finally anastomoses with the collateral radialis artery.

The ulnar artery (Fig. 68, No. 6 and 9) passes downward on the inner surface of the ulna to the carpal region where it gives off a branch to the wing plexus and divides into two branches, the smaller branch supplying the thumb (Fig. 68, No. 7). This branch passes down the radial side of the middle finger to the last joint of the second finger. The larger (Fig. 68, No. 8) lies between the second and the third finger bones, and passes through a slit between these two bones to the flexor side of the hand and extends to the last finger-joint, supplying the structures in the region. The ulnar artery gives off a small arterial twig to the papilla of each large wing feather (Fig. 67, No. 6).

The recurrent ulnar passes backward to the olecranon of the ulna and supplies the muscles, the skin, the feathers, and other structures of the region, and terminates in end collateral ulnar branches (Fig. 67, No. 5).

The posterior aorta (Fig. 63, No. 2) passes backward along the inferior part of the bodies of the dorsal and lumbo-sacral vertebræ. In the thoracic cavity it lies dorsal to the esophagus. It gives branches (esophageal) only to the esophagus during its passage as far as the seventh dorsal vertebra. Following this point there are given of several pairs of arteries which divide into a superior and an inferior branch. The superior branch extends upward and anastomoses with branches of the vertebral artery and other twigs coming from the intercostal arteries. These latter arteries given off are small dorsal arteries. The inferior branches extend downward between the ribs and supply the intercostal muscles. The intercostal arteries 225do not take their origin from the aorta in numerous and regular branches as in mammals; they consist originally of but few vessels, which are multiplied by anastomoses with each other and with the arteries which come out of the spinal canal. An arterial plexus is thus formed around the head of each rib, from which a vessel is sent to each of the intercostal muscles and ribs and are continued into the muscles upon the outside of the body and its integuments. The anastomosis of the intercostal arteries round the ribs is similar to the plexus, which is produced by the great sympathetic nerve in the same location. The lumbar arteries are given off farther posteriorly and along the lumbar region. The lumbar, like the dorsal branches are given off in pairs. These arterial branches pass along the thigh and the upper sacral vertebral region, and supply those parts. Ventrally they are covered by the kidneys and pass into the abdominal muscles. The posterior aorta gives off the spermatic arteries and the ovarian artery. In the male the former supply the testes. The ovarian artery of the female gives off a twig to each calyx containing an ovum. Each calyx is voluminously supplied with blood. Next the renal arteries are given off to the kidneys.

Fig. 63.—The vascular system injected. 1, The heart. 2, The posterior aorta. 3, The right brachio-cephalic artery. 4, The left brachio-cephalic artery. 5, The anterior mesenteric artery showing its many branches and anastomoses near and on the intestines. It is accompanied by branches of the mesenteric vein. 6, The rectal branch of the posterior mesenteric artery. 7, The duodenal loop and pancreas showing the pancreatic artery. 8, The anus. 9, The cloaca. 10, The liver. 11, The lungs. 12, The right subclavian artery. 13, The right carotid artery. 14, The right anterior vena cava. 15, The subclavian vein. 16, The right jugular vein. 17, The carotid trunk. 18, The posterior vena cava.

226

Fig. 64.—The splanchnic arteries, veins and nerves. 1, A portion of the left testes. 2, Adrenal gland. 3, Anterior lobe of kidney. 4, Heart. 5, Liver. 6, Second portion of the esophagus. 7, Proventriculus. 8, Gizzard. 9, Spleen. 10, Duodenal loop. 11, Pancreas. 12, Blind extremity of cæcum. 13, Floating portion of small intestine. 14, Rectum. 15, Cloaca. 16, Anus. 17, Celiac axis. 18, Ureter. 19, Vas deferens. 20, Recurrent sinister artery. 21, Anterior recurrent dexter artery. 22, Arteria hepatica dextra. 23, Recurrent esophageal artery. 24, Recurrent intestinalis artery. 25, Ilio-colicus artery. 26, Anterior mesenteric artery. 27, Recurrent branches of the same. 28, Ilio-cœliacus artery. 29, Recurrent superior hemorrhoidal artery. 30, Posterior mesenteric artery. 31, Crural arteries. 32, Sacralis media artery. 33, Recurrent renalis. 34, Middle renal lobe. 35, Posterior renal lobe. 36, Vena mesentericus communis. 37, Vena hemorrhoidalis. 38, Vena pancreatico-duodenalis. 39, Vena proventriculo-leinealis. 40, Vena portalis dextra. 41, Ischiadic nerve. 42, Thoracic sympathetic trunk. 43, Anterior splanchnic plexus. 44, Spinal nerves. 45, Posterior splanchnic nerve plexus. 46, Intestinal nerve trunk. 47, Vena renalis magna.

The celiac axis (Fig. 64, No. 17) originates near the seventh sternal vertebra and to the right of the esophagus, breaks through the diaphragm, and, near this point, gives off a recurrent esophageal (Fig. 64, No. 23). The celiac axis gives off three main branches: The anterior or recurrent dexter, the posterior or recurrent sinister, 227the recurrent intestinalis, all of which lie to the right of the spleen, under the left lobe of the liver, and along the left side of the stomach. The recurrent sinister (Fig. 64, No. 20) gives arterial branches to the proventriculus, the gizzard, the pyloris, and the left lobe of the liver. The anterior or recurrent dexter (Fig. 64, No. 21) gives off a renal artery and from four to six splenic arteries.

The recurrent intestinalis artery (Fig. 64, No. 24) arises on the posterior of the stomach within the duodenal loop, and supplies the duodenum and the pancreas (Fig. 63, No. 7). It gives off a branch, called the recurrent ilio-colicus (Fig. 64, No. 25), which supplies the large intestines, including the cæca.

The arteria hepatica dextra (Fig. 64, No. 22) is a branch from the celiac axial trunk. It gives several branches to the right lobe of the liver and to the gall-bladder. The gastric branches pass to the muscles of the stomach. The anterior and posterior recurrent branches often anastomose.

The anterior mesenteric artery (Fig. 63, No. 5; Fig. 64, No. 26) originates from the posterior aorta near the generative glands. It is directed downward, and divides into many branches which pass in the mesentery toward the intestines. Recurrent branches (Fig. 64, No. 27) are given off, which anastomose, forming mesenteric arches. From these arches are given off branches which supply the intestinal walls.

The anterior mesenteric artery gives off the recurrent ilio-celiacus (Fig. 64, No. 28) which is distributed to the cæca; other of its branches are distributed to the small intestine.

The anterior mesenteric artery extends along the small intestine and ends in the recurrent superior hemorrhoidal arteries (Fig. 64, No. 29) which anastomoses on the surface of the rectum with a branch of the posterior mesenteric artery.

Branches from the anterior mesenteric artery also anastomose with branches of the celiac axis.

The posterior mesenteric artery (Fig. 64, No. 30) is given off from the posterior aorta posterior to the origin of the anterior mesenteric and near the arteries of the thigh and is distributed to the lesser mesentery supplying the large intestine. Branches of the superior hemorrhoidal arteries anastomose with branches of the posterior mesenteric artery. Branches from this source are called the median hemorrhoidal (Fig. 63, No. 6).

The posterior mesenteric artery (Fig. 64, No. 30) also gives off a 228long branch to the cæca. Branches of the posterior mesenteric artery anastomose with branches of the anterior mesenteric.

The crural arteries (Fig. 64, No. 31) are given off in a pair from the posterior aorta. They pass through the mass of the lobes of the kidneys, at about the median region, and extend out of the pelvic cavity in front of the spine and ilio-pubic ligament.

Fig. 65.—Blood-vessels and nerves of the hind extremity. Inside view of leg. 1, Ischiadic nerve. 2, Ischiadic artery. 3, Posterior tibial vein. 4, Vena metatarsa dorsalis interna. 5, Vena metatarsalis plantaris profunda. 6, Vena cruralis. 7, Vena metatarsalis interna, vena magna. 8, Vena tibialis postica. 9, Vena metatarsa magna. 10, Nerves of the toes. 11, Vena metatarsalis dorsalis profunda.

The crural, or the external iliac artery, is divided into three branches as follows:

First, the internal pelvic, or umbilical artery, is given off just as the cruralis leaves the pelvic cavity. It passes, as a long vessel, on the inner surface of the lumbo-sacral bones and supplies the obturator internus muscle and extends into the umbilical region. It gives off branches to the abdominal muscles, and, in the female, a branch is distributed to the ligament of the oviduct.

Second, the arteria circumflex femoris, which passes between the sartorius and vastus internus and extends dorsalward, supplies the sartorius muscle, the vasti muscles, and the ilio-trochanteric region.

Third, the femoral artery, which passes beside the vena cruralis and extends down the posterior surface of the thigh to the knee-joint, supplies the upper thigh muscles with the exception of the adductor muscles.

229

Fig. 66.—Blood-vessels and nerves of the posterior extremity. Outside view. 1, Anterior tibial artery. 2, Metatarsal artery. 3, Digital arteries. 4, Vena cutaneous crurus. 5, Ischiadic artery. 6, Vena cruralis. 7, Lateral cutaneous branch of the ischiadic nerve.

Fig. 67.—Blood-vessels and nerves of the fore limb. Outside view. 1, Median nerve. 3, Ulnar nerve. 4, Radial artery. 5, Recurrent ulnaris artery. 6, Twigs of ulnar artery to wing feathers.

The ischiadic artery (Fig. 69, No. 9) forms the main artery of the posterior extremity. This artery, the largest vessel of that region, is given off from the posterior aorta and passes ventrally over and between two of the main lobes of the kidney. The continuation of the posterior aorta is called the sacralis media (Fig. 64, No. 32). The ischiadic artery gives off a recurrent renalis on the posterior lobe of the kidney (Fig. 64, No. 33). On the left side it gives off a branch to the oviduct and to the ligament of the oviduct. The main trunk leaves the cavity with the ischiadic nerve (Fig. 65, 230No. 1) through a foramen formed by the os ilium and the os ischium. It sends branches into the adductor muscles of the upper and the lower thigh. It gives off anastomotic branches which unite with those from the femoral artery. At the flexure of the knee-joint it gives off two branches to that region (Fig. 69, No. 10). It gives off another branch to the gastrocnemius muscle and one to the flexor perforans digitorum. It terminates in the anterior and posterior tibial arteries.

Fig. 68.—Blood-vessels and nerves of the fore limb. Inside view. 1, Vena humeri profunda. 2, Brachialis longus inferior. 3, Brachialis profunda. 4, Radial artery. 6, Ulnar artery. 7, Ulnar arterial branch to thumb. 8, Digital branch of ulnar artery. 9, Ulnar artery.

The first, the tibialis postica (Fig. 69, No. 12) passes between the gastrocnemius and the deep flexors giving off branches in its course to the skin and to other parts, and disappears shortly below the intertarsal joint.

The second, the tibialis antica (Fig. 66, No. 1; Fig. 69, No. 11), is often the larger of the two arteries. The anterior tibial artery gives off branches to the knee-joint and to adjacent structures. It gives a large branch to the head of the gastrocnemius muscle. It passes to the posterior surface of the tibial head and gives off the peroneal artery, which passes through the membrana interossea located between the tibia and fibula giving branches to the anterior side of the membrane of the patellar region of the knee-joint. It gives branches to the anterior side of the lower thigh and finally terminates subcutaneously in the anterior tibial plexus.

The main portion of the anterior tibial artery passes downward 231along the posterior surface of the membrane located between the tibia and fibula, and sends branches for the flexor digitorum communis et profundus. It then breaks through the membrane, reaches the anterior side and there communicates with the anterior tibial plexus. It gives off branches to the muscles on the anterior side of the lower thigh and the skin, and passes between the outer and the middle malleolus of the tarsal bones. It passes to the plantar surface and divides between the toes. In addition to the plantar branches there are given off dorsal branches between the third and the fourth toes. These branches form the direct continuation of the dorsal vessels of the anterior tibial plexus.

Fig. 69.—Blood-vessels and nerves of the femoro-tibial region. A section of the tibia removed.

A. Veins, arteries and nerves dissected as in B.

B. V, Vein. A, Artery. N, Nerve. 1, Vena poplitealis. 2, The three veins forming the vena poplitealis. 3, Vena femoris interna profunda. 4, Vena femoris anterior. 5, Vena cruralis. 6, Vena cutanea abdominalis femoralis. 7, Vena cutaneous cruralis. 8, Deep vein of the knee-joint. 9, Ischiadic artery. 10, Branches of ischiadic artery to flexure of knee. 11, Anterior tibial artery. 12, Posterior tibial artery. 13, Ischiadic nerve. 14, Trunk (a branch of the ischiadic) which gives off the superficialis peroneus and peroneus profundus. 15, Median branch of ischiadic nerve. 16, Superficialis peroneus. 17, Lateral branch of the ischiadic nerve.

The arteria pudenda communis (Fig. 70, No. 20) passes to the depressor coccygeus muscle, gives off a branch to the caudal part of the kidney, crosses the ureter, provides the ischio-pubic and pubio-coccygeus, or depressor coccygis lateralis, muscles, and on 232the lateral rim of the latter muscle it gives off the arteria hemorrhoidalis intima. This artery passes to the bursa of Fabricius and to the end of the cloaca. It enters into the ischio-coccygeus muscle, and divides into the arteria pudenda externa, and in ducks, the arteria profunda penis. These branches supply the vas deferens, the ureter, the cloaca, the penile structure, and the muscles of these parts.

Fig. 70.—Blood-vessels of a Cornish cock. 1, The left pulmonary artery. 2, Right pulmonary artery. 3, Left brachio-cephalic artery. 4, Left subclavian artery. 5, Left carotid artery. 6, Right brachio-cephalic artery. 7, Posterior aorta. 8, Posterior vena cava. 9, Left pulmonary vein. 10, Right pulmonary vein. 11, Celiac axis. 12, Anterior mesenteric artery. 13, Ischiadic artery. 14, Crop. 15, Superior artery of the crop and vein of same name. 16, Testicular or ovarian artery. 17, External iliac artery. 18, Intercostal nerve. 19, Median sacral artery. 20, Arteria pudenda communis. 21, Anus. 22, Vena hypogastrica. 23, Right vena hepatica magna. 24, Left vena hepatica magna. 25, Vena iliaca interna. 26, Vena iliaca communis. 27, Vena iliaca externa. 28, Vena coccygo-mesenterica. 29, Vena umbilicalis. 30, Vena suprarenalis. 31, Origin of the pars renalis. 32, Lumbar veins. 33, Vena epigastrica. 34, Lumbales (arteries). 35, Anterior division of the lumbo-sacral plexus. 36, Posterior division of the lumbo-sacral plexus. 37, Left anterior vena cava. 38, Right anterior vena cava.

The Sacralis Media.—The median coccygeal artery (Fig. 70, No. 19) forms the single extension of the sacralis media. It gives off lateral branches between the caudal vertebræ which supply the dorsal muscles of that region and the skin. The third pair are the largest. These are the arteriæ coccygeæ laterales, and are located on the dorsal side of the tail, they supply the tail glands and rudder feathers, the main tail feathers, or rectrices. A small arterial twig is given off to the papilla of each rectrix.

The venous blood enters the lungs from the right ventricle through the two pulmonary arteries (Fig. 70, No. 1 and 2).

The two pulmonary veins (Fig. 70, No. 9 and 10) collect the arterial blood from the lungs, and empty it into the left auricle.

There are three venæ cavæ which collect the systemic blood and empty it into the right auricle. These venæ cavæ are two anterior (Fig. 70, No. 37 and 38) and one posterior (Fig. 70, No. 8).

Each anterior vena cava is formed by the union of a vena jugularis, a vena vertebralis, and a vena subclavicularis (Fig. 63, No. 15).

Fig. 71.—Veins of the liver of a fowl. 1, Vena mesenterica communis. 2, Vena portalis propria. 3, Anterior vena mesentericus. 4, Vena portalis dexter. 5, Vena portalis sinister. 6, Posterior vena cava. 7, Celiac axis. 8, Base of the heart. 9, The liver. 10, Hepatic veins.

The jugular vein is formed by the union of the vena cephalica anterior, and the vena cephalica posterior.

The jugular vein (Fig. 62, No. B, 3) passes along the side of the neck and lies near the trachea, the esophagus, and the pneumogastric nerve. Near the base of the skull the two jugular veins, the right and the left, are connected by a transverse vein. By this anastomosis part of the blood from the left jugular vein is sent into the right. Therefore the right jugular vein is larger than the left. The jugular veins collect the blood from the tongue region, the thyroid, the esophagus, the trachea, the crop, and other structures along its course through the cervical region.

234The vertebral veins are divided into the anterior and the posterior, or the inferior and the superior. The anterior vertebral vein is located in the cervical region and collects the blood from the brain and the inner part of the head. The vertebral vein passes along the dorsal side of the spinal cord.

The posterior vertebral vein is located in the dorsal region, passes backward and receives the blood from the dorsal neck region and from the intercostal veins and from the vertebral segments and adjacent regions.

The anterior and the posterior vertebral vein form one trunk, the vertebral vein, and this trunk empties into the vena jugularis just before the subclavian and the jugular unite.

The subclavian vein collects the blood from the anterior extremities. It unites with the vena jugularis of the same side.

The left vena cava receives the coronary veins from the heart.

The vena facialis interna (Fig. 62, No. 12) lies dorsal on the pterygoid bone and receives the vena maxillaris, the vena ophthalmica, the vena mandibularis interna, the venæ pharyngeæ superiores, and the vena retis mirabilis temporale.

Fig. 72.—Blood-vessels and nerves of the abdominal cavity and hind extremity and head. 1, Vena renalis. 2, Vena intervertebrales sacrales. 3, Posterior aorta. 4, External iliac. 6, Ischiadic nerve. 7, Ischiadic artery. 8, Arterial rete (plexus temporalis). 9, Ophthalmic artery. 10, Palatine artery. 11, Lingual artery. 12, Hyoid artery. 13, 14, External carotid artery. 15, Internal maxillary artery. 16, Superior laryngeal artery. 17, Superior esophageal artery. 18, Occipital artery. 19, Internal carotid artery.

The vena maxillaris comes out of the upper beak with the recurrent trigeminus nerve and then passes backward between the jugular and palatine bones. It lies medio-ventrally to the eyeball and communicates at this point with the ophthalmic vein. It is covered ventrally with the pterygoid bone. The maxillary vein collects the blood from the gland of Harder, the upper beak, and 236receives blood from the vena supra-palatina and from the lower jaw bone and the external mandibular vein. It also receives blood from the external sublingual vein, and the sublingual gland. It follows the inner rim of the jaw bone. The maxillary vein receives an anastomosing branch from the cutaneous facial vein, at a point near the commissure of the mouth.

Fig. 73.—Photograph of blood-vessels and nerves of the thorax. 1, Vena sternalis. 2, Vena thoracico-externa. 3, External thoracic artery. 4, Coracoid bone. 5, Sternum. 6, Shoulder-joint. 7, Humerus. 8, Clavicularis artery. 9, Sterno-clavicularis artery. 10, Thoracico-humeralis artery. 11, Subclavian artery. 12, Axillary artery. 13, Brachialis profundus artery. 14, Ulnar artery. 15, Radial artery. 16, Internal mammary artery. 17, Superior vein of the crop. 18, Superior artery of the crop. 19, Brachial nerve plexus. 20, Anterior division of brachial nerve plexus. 21, Posterior division of brachial nerve plexus.

The vena ophthalmica lies close to the point where the olfactory nerve passes out of the cranial cavity. The largest branch it receives is the recurrent ophthalmo-temporalis, which accompanies the lateral side of the optic nerve. It collects the blood from the base of the brain, from Harder’s gland, from the eye muscles, from the 237inner eye, the nose, the lacrimal gland, the skin of the frontal region, and the comb.

The trunk of the internal facial vein receives the blood of the internal mandibular vein. The internal mandibular vein emerges from the alveolar canal of the inferior jaw bone and receives branches from the muscles of mastication.

The vena retis mirabilis temporalis passes out of the eye cavity and lies between the internal facial vein and the external facial vein, and passes around the os quadratum and the os pterygoideum. It receives veins from the outer ear region, lacrimal gland, eyelids, and the spheno-temporalis.

238The venæ pharyngeæ superiores are the veins on the dorsal surface of the pharynx. These veins form the small plexuses which unite with the two trunks of the facial veins. This forms an anastomosis between the left and the right facial veins.

The vena facialis externa (Fig. 62, No. B, 9) lies behind the quadrate bone and is partly covered ventrally by the inner extension of the lower jaw bone. It collects the blood principally from the upper region of the cranium and the face, including the comb.

The vena facialis cutinea receives branches from the muscles in the region of the jaw, the lower jaw bone, the muscles of the eyelids, the frontal region, and the anastomotic branches from the vena maxillaris.

The vena temporalis is made up of veins from the skin of the temporal region, the masseter and the tongue muscles, and from the sides of the upper throat region.

The vena palpebralis is made up from veins from the three eyelids and the temporal region near the eye. Its trunk passes laterally over the temporo-mandibularis ligament. The vena palpebralis collects blood from the lacrimal gland, the eyelids, and the outer ear region.

The following veins empty into the trunk of the vena facialis communis: venæ pharyngis superiores, vena muscularis depressoris mandibulæ, vena muscularis colli anterior superioris, vena lingualis et hyoidea. The right terminal branches of the vena lingualis empty into the vena cephalica posterior.

The venæ pharyngis superiores and vena lingualis et hyoidea collect blood from the muscles of the tongue and posterior tongue region.

The vena lingualis et hyoidea (Fig. 62, No. B, 7) collects the blood from the muscles of the tongue region, the lower tongue glands, and the upper throat region.

Between the two trunks of the vena facialis communis and anterior to the entrance of the vena cephalica posterior there is an anastomosis, the vena transversus (Fig. 62, No. B, 5). Through this anastomosis which lies crosswise the two jugular veins are influenced in different ways. At this point both jugular veins are of the same size. The anastomotic branch lies crosswise. Through this anastomosis the 239right receives some blood from the left head region indicating that the blood flows from left to right. This, as stated before, makes the left jugular vein the smaller.

The left vena cephalica posterior (Fig. 62, No. B, 8) communicates with the transverse vein (Fig. 62, No. B, 5). The left receives the smaller veins of the skin region, the esophagus, and the trachea. These vessels communicate with their fellow of the opposite side and with the vertebral vein of the same side, which causes a gradual reduction of the size of the jugular vein.

The vena cephalica posterior (Fig. 62, No. B, 8) is formed from the veins of the sinuses of the cranium, the brain, the vena auris, the vena jugularis prima, the vena carotis, and the vena occipitalis. It collects most of the blood from the cranium and the posterior part of the head and from the tongue.

The sinus longitudinalis (Fig. 62, A, 10) extends from the dorsal median line of the internal occipital protuberance to the olfactory 240nerve. It collects the blood from the choroidea of the brain and from the skin of the frontal region. It receives laterally the veins of the nose, the vena ophthalmica, and the sinus transversus.

The sinus occipitalis (Fig. 62, No. A, 4) forms the continuation of the transverse sinus. It is located in the posterior cerebral cavity, and is wing-shaped, extending both to the right and to the left.

The sinus foraminis occipitalis a continuation of the sinus occipitalis, lies transversely on the ventral side of the cranial cavity and receives the veins from the medulla oblongata. One branch passes through the os occipitalis basilare, and then extends sidewise to the foramen magnum and anastomoses with the vena occipitalis.

The sinus transversus (Fig. 62, No. A, 6) extends in a pair from the internal occipital protuberance between the cerebrum, cerebellum, and the corpus quadrigeminum. It receives vessels from the upper surface of the cerebellum. The sinus has three branches, all of which empty into the sinus semicircularis.

The sinus semicircularis extends along the dorsal petrosal rim, anterior to the inner ear, and from this point backward. Near the foramen magnum it passes through the os occipitale and empties into the external occipital vein.

The vena occipitalis externus extends near the foramen magnum, surrounds the basis occipitalis, and receives the semicircular sinus and through the semicircular sinus the blood from the sinus transversus.

The sinus petrosus sphenoideus, passing in company with the occipital sinus, extends from the transverse sinus to the cavity near which the trigeminus lies. The sinus dividing into two branches, one of these extends to the hypophysis and unites with the basal veins of the brain; the other passes with the rete out of the cranial cavity along with a branch of the trigeminus, and communicates with the rete mirabile temporale.

The sinus temporo-sphenoideus (Fig. 62, No. A, 5) extends forward and outward from the transverse sinus, and, between the corpus quadrigeminum and the cerebrum, unites with the sinus venosus annularis basilaris.

The sinus venosus annularis basilaris lies in the region of the optic nerve and surrounds the hypophysis, forming a complete circle. It receives small vessels from the cerebrum, the corpora quadrigemina, 241and anteriorly the longitudinal basilar vein or vena basilaris media, of the cerebrum, which comes out of the anterior annular venous sinus. The anterior annular venous sinus surrounds the base of the olfactory nerves. It communicates with the sinus petrosus sphenoideus, which emerges from behind the optic lobe, the sinus temporo-sphenoideus, which emerges from in front of the optic lobe, and posteriorly the median longitudinal vein of the medulla oblongata or vena basilaris. Laterally and anterior to the optic lobe it receives the vena basilaris lateralis, and also a branch of the vena ophthalmica.

The blood received by the sinus annularis basilaris comes from the brain cavity through three pairs of veins, as follows: first, the two ophthalmic veins which pass through the posterior orbital wall between the olfactory and the optic nerve; second, two other branches of the ophthalmica which pass with the optic nerve; third, two veins which pass through a foramen by the side of the sella turcica to the hypophysis together with the carotis cerebralis, and then leave the cerebral cavity ventrally, at which point they are called the venæ carotes. These last accompany the cerebral artery backward, and pass through a foramen in the base of the cranium. Each one then passes through the cranial wall close to the external auditory canal, and empties into another vein in the posterior region of the head.

The sinus fovæ hemispherii cerebelli lies in the hollow between the os petrosum and the semicircular canals. It receives blood from the external occipital sinus and from the cerebellum, and empties into the vena auris interna.

The vena auris interna passes through a bony canal along the outer rim of the posterior semicircular canal and then along the external semicircular canal. It receives vessels from the labyrinth, and extends along the posterior rim of the tympanum to the outer ear canal.

The vena occipitalis interna, extending from the sinus foraminis occipitalis, passes through the side of the atlas and divides near the condyle into two branches. One of these branches the internal occipital, forms the root of the vena vertebralis, and the other empties into the vena occipitalis externa.

242Near the outer and upper part of the condyle it forms two large veins and collects the blood from the vena occipitalis media. These veins collect the blood from the rectus capitis anticus, and communicate with the vena cephalica anterior.

The vena occipitalis externa, sometimes called the vena occipitalis collateralis, extends from the vena auris, and receives vessels from the neck region. It receives on the side of the occipitoatloid joint the vena occipitalis interna. The vena occipitalis externa forms a junction with the vena vertebralis emptying into the transverse vein.

The trunks of the vena jugularis or vena cephalica communis pass subcutaneously on both sides near the trachea and the esophagus. Near the height of the thyroid gland they almost touch the carotid artery. They then cross, dorsalward, the trunk of the subclavian artery, and in their course receive the vertebral vein and unite with the subclavian vein toward the side of the vena brachiocephalica. The union on the right side lies to the right of the anterior aorta, and the union on the left side lies to the left of the pulmonary artery.

The jugular vein (Fig. 18, No. 4) receives in its course the following veins:

The venæ linguales (Fig. 62, No. B, 7), which at times empty into the vena cephalica posterior.

The vena occipito-collares, which arises on the ventral side from the muscles of the neck and the vertebræ; empties into the vena occipitalis lateralis and also communicates with the vena jugularis by anastomoses.

The venæ ascendentes laterales, which collect blood from the lateral sides of the neck.

The venæ colli cutineæ, which enter the jugular vein laterally. The upper branches are directed crosswise, and are shorter than the lower ones. The lower branches are located near the thorax, are directed upward, and anastomose by fine terminal twigs. Plexuses are frequently formed in the inner side of the skin of the neck.

The venæ esophageæ are numerous smaller veins formed in closely woven plexuses in the region of the esophagus along the neck. Some pass upward and some downward.

The venæ tracheales are located on the supero-lateral side of the trachea and along the edge of the lateral tracheal muscle. They have numerous anastomoses transversely with the longitudinal vein of the cervical region, anteriorly with the vena lingualis, and on the left side with the left jugular vein.

The vena subscapularis passes along the median line of the scapula to the side of the jugular vein, and anastomoses with the vertebral vein.

The venæ glandularum thyroidearum are several small, short veins coming from the thyroid gland.

The vena vertebralis, originating near the atlas, is a continuation of the internal occipital vein. The internal occipital vein receives the bulk of the blood from the brain and communicates with the lateral veins of the cervical region and collects blood from the cervical vertebra. The vertebral vein accompanies the vertebral artery and the deep sympathetic nerve trunk in the vertebral canal. The vein either leaves this canal with the vertebral artery at a point near the last two vertebral nerve trunks of the brachial plexus, or it leaves the canal one vertebra in front of the vertebral artery.

The vena vertebralis lateralis dorsalis collects blood from the cervical vertebræ, from the dorsal vertebræ, and from the intercostal region.

244The blood from the neural canal, including the spinal cord, is collected in one long vein extending from the head to the tail on the upper side of the cord. This vein has sinus-like expansions. Between each two vertebræ it anastomoses with the vertebral vein on each side. In the lumbo-sacral region these anastomotic branches empty into the hypogastric veins.

The vena intercostalis is formed in the costal region and anastomoses with the vein extending longitudinally between the capitulum and the tuberculum of the rib.

The vena vertebralis posterior at the height of the first and the second dorsal vertebræ, empties into the main trunk of the vertebral vein. Its lower roots come out near the side of the kidney, and unite, forming a large ascending trunk uniting with the vena vertebralis anterior forming one large trunk, which extends into the chest cavity.

The posterior vertebral vein also receives a large vein from the skin of the outer tarsal region and a few vessels from the muscles of the outer abdominal and the outer costal region, from the skin, from the pectoralis muscles, and from the shoulder region.

The vena thoracica externa (Fig. 73, No. 2) is made up of veins mainly from the pectoral group of muscles. The posterior branch anastomoses with the vena cutinea. Its anterior branch is made up mainly of branches from the furcular region. It empties into the vena pectoralis externa and the vena pectoralis externa empties into the vena subclavia.

The vena coracoidea comes out of the region of the shoulder-joint, passes downward along the inner surface of the coracoid, and receives small branches from the walls of the arteria brachia cephalica and from the pericardium.

The vena sternalis (Fig. 73, No. 1) is made up of two branches. The outer branch comes from the muscles of the subclavian region passes over the cristi sterni, medially, to the sterno-coracoid joint and into the breast cavity, where it receives the inner branch, which drains the inner surface of the breast-bone.

The vena thoracica interna empties into the vena cava anterior. It extends from the abdominal muscles where it communicates with 245the epigastric vein. It then passes on the inner side of the thoracic cavity close to the breast-bone and receives many intercostal veins.

The vena cava sinistra receives first, the vena proventricularis communis, which collects the blood from the walls of the proventriculus, and second, the vena coronaria cardis magna. This latter vein originates close to the apex of the heart and collects blood principally from the walls of the left ventricle. It connects in the left sulcus transversus with the vena cardis superior and ends at the base of the left upper vena cava. Its exit is not guarded by a valve. The veins of the right ventricle are partly on the surface. They collect blood along the sulcus transversus dexter and enter directly into the right ventricle. The veins of the front part of the heart are small. They collect behind the sulcus coronalis and end either directly into the right auricle or into the vena cardis magna.

The vena radialis profunda accompanies the radial artery on the dorsal anterior rim of the index-finger and passes, on the dorsal side, over the carpal region. It passes through the interosseous ligament between the ulna and the radius, and reaches the ventral surface of the arm. At this point it passes upward and anastomoses with the vena ulnaris. It collects the blood from the skin of the anterior wing region and the flexor muscles of the anterior arm. It empties into the vena brachialis.

The vena humeri profunda (Fig. 68, No. 1) emerges at the height of the elbow, and collects blood from the skin of the dorsal surface of the wing. It also receives veins from the muscles of the posterior side of the upper arm. It passes subcutaneously and dorsally over the dorsal portion of the humerus in company with the external radial muscle and passes with it around the external part of the humerus between the long and short heads of the triceps. It takes a diagonal course to the shoulder cavity and at that point empties into the brachial trunk.

The profundus ulnaris originates at the volar surface of the hand, proceeds in company with the ulnar artery, and sends on the base of the hand small anastomotic veins to the vena cutanea ulnaris or basilica. It passes along the anterior arm and between the flexor carpi ulnaris and the pronator profundus muscle to the elbow-joint. On the median surface of the biceps it passes upward and anastomoses 246with the radial vein. The ulnar vein, in the region of the elbow-joint, receives a large lateral branch which extends around the end tendon of the biceps and anastomoses above with the vena basilica.

The vena basilica or cutanea ulnaris is a long vein which originates from the subcutaneous dorsal surface of the index-finger. Near the base of the hand it receives an anastomosing branch from the vena radialis and the vena ulnaris, and then passes upward along the posterior rim of the ulna. It receives numerous branches from the roots of the flight feathers. It crosses below the elbow-joint and reaches the volar surface of the arm. It receives a large branch from the ulnar vein, and then, passing in a diagonal and median direction to the triceps, extends to the shoulder cavity where it empties into the axillary vein.

The outer breast veins unite forming a trunk which crosses ventrally to the subclavian artery, and empties into the subclavian vein.

The vena cutanea abdomino-pectoralis collects the blood from a large skin area of the abdomen, the upper thigh, the breast, and the intercostal region. In the skin of the abdomen it forms a network.

The main trunk passes in the median abdominal line forward and then upward, along the outer edge of the pectoralis major, over the first sternal rib; receives blood from the infrascapular vein, and empties into the pectoralis externa.

The vena brachialis is located in the middle of the humerus and 247the triceps muscle. It is formed by the vena ulnaris, and the vena radialis. It passes with the median nerve and the brachial artery over the inner surface of the humeral joint. Posterior to the humeral head it receives the vena profunda humeri. At the shoulder cavity it receives the vena cutanea ulnaris or vena basilica.

The trunk of the axillary vein is very short and is formed by the veins of the shoulder and the wing. The deeper wing veins accompany the large arterial and the nerve trunks.

The posterior vena cava (Fig. 63, No. 18; Fig. 70, No. 8) has its origin in the posterior half of the body of the bird, somewhat to the right of the posterior aorta, near the anterior lobe of the kidney, by the union of the right and the left vena iliaca communis. It receives the blood from all of the posterior half of the body including the posterior limbs, of the visceral organs, of the abdominal and the pelvic cavity. The posterior vena cava passes dorsally through the right lobe of the liver and through the diaphragm and ends in a short, broad trunk on the posterior dorsal side of the right auricle of the heart. Its opening into the heart is guarded by two half-moon 248shaped valves. The basal part of the trunk reaches from the right auricle of the heart to the upper anterior rim of the liver where it receives three large trunks, first, the right and second, the left vena portalis hepatica magna, and third, smaller vessels from the liver substance.

In the skin region on the inner sides of the toes near their bases the small veins collect into five metatarsal veins. The largest vein collects the blood from the first, the second, and the third toe, passes up the tarsus and is called the vena metatarsalis interna, or vena magna (Fig. 65, No. 7). It is located just beneath the skin on the inner surface of the metatarsal bone. It passes in a circle, around the condyle of the tibia and becomes the vena tibialis postica (Fig. 65, No. 3 and 8). The vena tibialis postica passes under the tendon Achillis and the tendon of the flexor digitorum brevis, lies subcutaneously upon the latter, and reaching the knee-joint crosses over the upper surface of the ischiadic nerve and becomes the vena poplitealis, at which point it receives the vena tibialis antica.

249On the dorsal side of the metatarsus are two veins. The vena metatarsalis dorsalis profunda (Fig. 65, No. 11), which extends under the tendon of the extensors of the toes, along with the artery and the nerve. It collects the blood from the third and the fourth toe and in the middle of the metatarsus receives the vena metatarsalis dorsalis interna (Fig. 65, No. 4), which connects the vena metatarsalis dorsalis profunda and the vena magna. The two dorsal veins anastomose with the vena magna, at the intertarsal joint. They pass transversely under the ligament and form the main trunk of the vena tibialis antica which lies close to the anterior surface of the tibia. Near this point there is formed a plexus of veins which again form a trunk and communicates with the vena peronealis and enters between the tibia and fibula with the tibialis antica. It extends along the flexure of the knee and the posterior part of the lower thigh.

The vena metatarsalis externa passes subcutaneously on the outside of the fourth toe and the metatarsus, and above the intertarsal point joins the tibialis postica.

The vena metatarsalis plantaris profunda (Fig. 65, No. 5) lies on the ventral side of the foot and forms several anastomosing arches with the other veins of the toes. Below the intertarsal joint it enters the vena metatarsalis magna (Fig. 65, No. 9).

The vena cutanea cruralis (Fig. 69, No. 7) originates at the height of the tarsal region and passes subcutaneously on the outer posterior surface of the lower thigh region to the vena poplitealis.

The venæ surales or inferior muscular branches of the vena poplitealis consist of many veins. One branch comes from the region of the shank and from the gastrocnemius muscle; another as a main branch from the posterior surface of the lower thigh; and a third from the outer surface of the muscles and skin of the upper thigh. The three branches together with the anterior and posterior tibial (Fig. 69, No. 2) unite at the flexure of the knee forming the vena poplitealis (Fig. 69, No. 1).

In the region of the upper thigh, between the knee and the abdominal cavity, the following four veins form the vena cruralis: (Fig. 66, No. 6; Fig. 69, No. 5). First, the vena cutanea abdominalis femoralis (Fig. 69, No. 6) which comes out of the side of the abdominal 250wall, draining the skin of the inner surface of the upper portion of the thigh, the adductor muscles, and the region of the abdominal and the breast border. It crosses the ischiadic artery in a diagonal direction, and enters the vena cruralis in the middle of the crural region.

Second, the vena femoralis interna profunda (Fig. 69, No. 3) forms a communication between the end of the suralis near the knee. It lies on the median portion of the flexor cruris internus muscle.

Third, the vena femoralis anterior (Fig. 69, No. 4) is formed from branches from the sartorius and adjacent structures, and anteriorly empties into the crural vein near where the latter enters the abdominal cavity.

Fourth, the vena epigastrica (Fig. 70, No. 33) is formed by branches from the abdominal wall and branches from the walls of the abdominal air-sacs. It passes along the median surface of the os pubis and ends into the vena cruralis near the spine of the ilio-pubica or at a point where these join with the vena hypogastrica.

The vena iliaca interna or the vena hypogastrica (Fig. 70, No. 22) collects most of the blood from the tail. The vena iliaca interna collects most of the blood from the pelvic cavity, and the adjacent intestines. It unites with the vena iliaca externa (Fig. 70, No. 27) and receives the vena renalis magna and forms the trunk of the vena iliaca communis (Fig. 70, No. 26).

The vena coccygea originates between the coccygeal vertebræ, and collects the blood from the region of the tail, including the tail feathers, the tail muscles, the tail gland, and the skin of the region. These small collecting vessels form a trunk on each side of the coccyx. The right and the left pass laterally, each one taking up a vena cutanea et pudenda, and frequently anastomosing with the vessels on the other side. These often unite into one vessel. Both trunks are connected by a transverse, or anastomotic, vessel. At this anastomosis there empty into it the vena coccygea mesenterica and the vena portalis. There also communicate at this point the right and the left hypogastrica caudalis. In its course it is partly imbedded in the kidney and passes anteriorly to the vena iliaca communis. This circle is called the arcus hypogastricus. Thus the 251veins of the abdominal cavity have many anastomoses forming many arcs, making possible two outlets for the blood.

The azygos sacralis empties into the arcus at about its middle. From here it extends forward to the inside and under the kidney and empties into the vena suprarenalis externa.

The vena cutanea pubica originates on the lower portion of the abdomen, collects the blood from the muscles of the distal part of the ischium, and enters the pelvic cavity between the ischium and the ilium. It joins with the vena cutanea caudalis.

The vena cutanea caudalis originates from branches which drain the skin and other parts of the ventral coccygeal region. The vena cutanea pubica also communicates with the vena caudalis muscularis and with the vena pudenda, thus forming the caudal trunk of the vena hypogastrica.

The vena pudenda originates in the walls of the cloaca in the region of the generative organs.

A small vena spermatica accompanies the lower end of the vas deferens and the ureter, and empties medially into the vena pudenda.

The pars renalis of the vena hypogastrica extends from the middle of the arcus to the union of the vena hypogastrica and the vena cruralis.

The vena hypogastrica communicates with the pars renalis. The vessels that empty into the pars renalis are as follows:

The venæ sacrales collect blood from the dorsal wall of the abdominal cavity and enter the pelvis through the foramen sacralis. They pass between the pelvic wall and kidney, and at times pass through the kidney tissue. They empty into the pars renalis of the hypogastric arch.

The venæ intervertebrales sacrales (Fig. 72, No. 2) originate in the region of the roots of the plexus of sacral nerves and pass through the kidney substance or on the dorsal surface and empty into the pars renalis.

The venæ renales (Fig. 72, No. 1) are very numerous and originate in the kidney substance, forming two main and several minor branches, which pass posteriorly, and empty partly into the vena hypogastrica, partly into the vena renalis magna, and also into the vena intervertebralis; other branches empty into the trunk of the iliaca communis.

The vena suprarenalis externa (Fig. 70, No. 30) is located near the anterior rim of the kidney and is connected with the vena 252hypogastrica. It also receives on the medial side, short branches which come out of the upper kidney surface and sacral vertebræ.

The vena ischiatica originates by the union of several venous branches which come from the muscles of the pelvis and upper thigh region. The ischiatic vein enters the pelvic cavity along with the ischiatic nerve and artery, and communicates with the vena hypogastrica at about the level of the anterior lobe of the kidney. It is always smaller than the vena cruralis.

The vena obturatoria originates mainly from vessels from the obturator muscles. It enters the pelvic cavity through the obturator foramen. Another branch is sometimes found which comes out of the inner surface of the peritoneum which covers the obturator muscles and the walls of the abdominal air-sacs and empties between the vena ischiatica and the vena vertebralis into the vena hypogastrica.

The vena intervertebralis lumbalis, which comes out of the lumbar region, the spinal canal, the lumbo-sacral nerve plexus, and several small venous branches from the lobes of the kidney. It passes dorsalward through the kidney and empties into the iliac vein. There are also communications with the vena intervertebralis thoracica.

The vena renalis magna (Fig. 64, No. 47) forms the main descending vein to the middle and posterior lobes of the kidney. It lies ventrally and mesially on the middle lobe and partly on the inner part of the posterior lobe. It sometimes has on each side two main trunks. The vein receives some small vessels out of the anterior kidney lobe, also other small veins from that part of the peritoneum which covers the kidney, from the rectum and finally small veins from the ureter.

The venæ testiculæ, or the vena ovariana drain the blood from the testicles of the male and ovary of the female. The size of these veins change with the enlargement of the testes or of the ovary during reproductive activity.

The venæ suprarenales revehentes are short, thick trunks coming from the adrenal glands. The left empties into the left side of 253the posterior vena cava and the right into the right dorsal side. These receive veins from the testicles in the male and from the ovary in the female.

The vena proventricularis inferior drains the stomach wall. One branch of this vein enters the left side of the posterior vena cava; the other enters the vena proventricularis communis, which in turn empties into the trunk of the anterior vena cava sinistra.

The venæ hepaticæ consist of one large and several small veins from each lobe of the liver, and empty into the posterior vena cava.

Some small vessels come from the pericardium and the peritoneal covering of the liver, and pass in the mediastinum to the trunk of the posterior vena cava.

In the region of the vena portalis:

The liver receives almost all the blood from the stomach, the intestines, the pancreatic gland, the spleen, partly from the liver itself, and partly from the abdominal air-sacs. This blood enters into the liver through the vena portalis dextra, the vena portalis sinistra, and the vena portalis propria.

In both lobes of the liver these veins divide into numerous small branches and collect again into two large short trunks, the vena hepatica magna dextra (Fig. 70, No. 23), coming out of the right lobe of the liver and the vena hepatica magna sinistra (Fig. 70, No. 24) coming out of the left lobe. These two vessels empty inferiorly into the posterior vena cava.

The vena portalis dextra receives the blood from the vena mesenterica communis.

The vena mesenterica communis (Fig. 64, No. 36) receives the blood from the vena coccygo-mesenterica (Fig. 70, No. 28) which comes from the arcus hypogastricus and receives the vena hemorrhoidalis (Fig. 64, No. 37). This drains the cloaca and the bursa of Fabricius, and it also receives veins from the rectum and from the base of the cæca.

The vena mesenterica anterior (Fig. 71, No. 3) accompanies the anterior mesenteric artery, and collects the blood from numerous vessels from the small intestine.

The vena pancreatico-duodenalis (Fig. 64, No. 38) comes out of the duodenum and the pancreas, along the right side of the stomach and along both cæca.

The vena proventriculo-lienalis (Fig. 64, No. 39) comes out of 254the dorsal side of the proventriculus on the left side of the gizzard, passes along the hilus of the spleen, and takes up several splenic veins.

The vena portalis dextra (Fig. 64, No. 40; Fig. 71, No. 4) receives a vein near the base of the gall-bladder. This branch enters the right lobe of the liver and unites with the vena portalis sinistra.

The vena portalis sinistra (Fig. 71, No. 5) enters the left lobe of the liver and there forms a sinus. It receives vessels which come from the muscles of the gizzard, the inferior vena proventricularis, and from the proventricular wall.

The vena portalis propria receives small veins which come out of the walls of the abdominal air-sacs and from the fat of the abdominal walls.

The vena umbilicalis originates in the umbilical region and empties into the vena hepatica magna sinistra at a point where it comes out of the liver (Fig. 70, No. 29). This is the remains of an embryonal vein which collected all the blood of the yolk sac, passed on the left side of the large intestine to the body, took up the vena mesenterica and ended as the vena umphalo-mesenterica.

The peculiarity of the lymph vessels is that they are associated with organs in which lymph cells are formed.

The lymphatic system consists of the lymph vessels and the cell-forming organs. In some instances the cell-producing organs are lymph follicles and in others lymph glands. For the most part the glands are replaced by plexuses which in many places surround the blood-vessels.

The lymph of birds is similar to that of mammals. The larger lymph vessels are similar to the veins, although the walls are always thinner. Its tunica intima is rich in elastic fibers and has a layer of endothelial cells on the inner side. The tunica media is formed of rings of smooth muscle fibers. The adventitia is composed of loose connective tissue.

The lymph vessels frequently form plexuses. The large lymph trunks follow the course of the larger blood-vessels, and frequently surround the arteries. All the lymph vessels of the body, exclusive of the lymph of the caudal region, form into a large trunk which originates on both sides of the celiaca communis and passes upward 255along the side of the abdominal aorta, reaching a point anterior to the celiaca. By receiving many vessels in this region it forms a plexus around the aorta, and finally divides into two vessels, the right and the left, ducti thoracici.

The lymph vessels of the left side of the head, the neck, and the lung, and the left wing, and also lymph vessels of the proventriculus and the throat enter into the left ductus thoracicus. They accompany the jugular vein and are closely associated with the thyroid gland.

The right thoracic duct receives the lymph veins from the right cervical lymph vein, and the right side of the head, the neck, the lung, and from the right wing.

After the right cervical lymph vein has passed through the right thyroid gland, it divides into two branches, one branch emptying into the right thoracic duct and the other into the vena cava dextra.

The lymph vessels of the liver, the stomach, the pancreas, and the duodenum enter near the root of the arteria celiaca into the large lymph trunk. The lymph vessels of the remainder of the intestines, of the kidney, and of the generative organs empty farther caudally.

The lymph vessels of the intestines take up the emulsified fat. This emulsion in birds is colorless. The vessels pass upward along the mesenteric arteries. There are no mesenteric glands. These vessels form a plexus around the arteria celiaca. The lymph vessels of the posterior extremities accompany the artery, especially the anterior iliaca externa, and empty into the thoracic duct at the point of the anterior iliaco-communis.

The lymph vessels in birds are numerous. The lymph glands are few. They are only visibly found in the anterior breast and the neck region, and sometimes in the wings. Lymph follicles are numerous in the intestines.

The thin walls of the lacteals, of the lymph vessels, and of the thoracic duct are made up of two tunics, the inner being the thinner and weaker.

The lymphatics of the foot unite to form the vessels along the sides of each toe. In palmipedes there are anastomosing branches which pass from the lateral vessels of one toe to those of the adjoining toe, forming arches in the uniting web of the foot. These branches form a small plexus at the anterior part of the digito-metatarsal joint, from which pass three or four lymph vessels. The anterior and 256internal branches accompany and form a network around the blood-vessels. The posterior and external branches receive the lymphatic vessels from the sole of the foot. They then ascend along the metatarsus and form, at its proximal articulation, a close network from which vessels pass along the tibial region, forming a plexus around it as far as the middle of the leg. From this there arises two branches. The smaller passes along the anterior part of the depression between the tibia and the fibula, as far as the knee-joint, where it joins the other branch, which accompanies the blood-vessel. The trunk formed by the union of these two vessels accompanies the femoral vessels. Forming plexuses in its course, it receives tributary vessels from the adjacent muscles. The iliac trunk accompanies the femoral vein into the abdominal cavity, entering just in front of the anterior end of the pubis. At this point it receives branches from the lateral parts of the pelvis and then separates into two branches. The posterior vessel receives some lymph from the anterior lobes of the kidney, and from the ovary, or testis, and communicates anteriorly with a branch formed by the lymph vessels adjacent to the anterior mesenteric artery, and posteriorly with a large vesicular plexus surrounding the aorta and its branches. This plexus receives the lymph from the renal plexus and from those accompanying the arteria media.

There are two sacral or pelvic vesicles which are situated at the angle between the tail and the thigh in the posterior part of the abdominal cavity. Each vesicle is a trifle more than a half inch long and a quarter inch wide, and is shaped somewhat like a kidney bean. They have muscular coats with striated fibers. These sacs are called “lymph hearts.”

The anterior division of the femoral lymphatic trunk accompanies the aorta, on which it forms a plexus with the branches of the opposite side, and with the intestinal lymph vessels. These vessels commence from a continuous plexiform network located between the mucous and the muscular coat of the intestine. They are larger at this point than where they leave the intestine to pass through the mesentery. They accompany the trunk of the anterior mesenteric artery and form a plexus around it.

Before reaching the region of the aorta, the intestinal lymphatic vessels communicate with the posterior division of the femoral trunk and with the lymph vessels of the ovary or of the testis. After passing to the region of the aorta they receive vessels from 257the pancreas and the duodenum, and terminate around the celiac axis with the lymphatics of the liver, the proventriculus, the gizzard, and the spleen, forming a rather voluminous plexus (Lauth).

The aortic plexus represents the receptaculum chyli and gives origin to two thoracic ducts, mentioned above, which passing on each side of the bodies of the vertebræ, pass one right and one left, over the lungs, from which they receive lymph vessels, and terminate after receiving the lymph vessels of the wing, into the jugular vein of their respective sides. The left thoracic duct, before emptying into the vein, receives the trunk of the lymphatics of the left side of the neck, and the right duct that of the right side of the neck, each tributary collecting lymph from all the structures of its side.

The lymphatics of the wing follow the course of the brachial artery, forming a plexus around it. These vessels are well developed in the elbow region. The principal trunk, following the humerus, receives collateral branches in its upper third. This vessel, when nearing the chest, receives two or three large lymph vessels from the pectoral muscles, and a branch which accompanies the brachial plexus.

The lymph vessels of the head accompany the branches of the jugular vein, collecting the lymph from the structures of the head and the neck.

The lymphatic vessels communicate at the anterior and posterior oblique anastomosing vessels. At the lower part of the neck each trunk receives a vessel, which accompanies the carotid arteries. Further on they are provided with a lymph gland which rests on the jugular vein.

The special function of the blood is to nourish all the tissues of the body, and in this way to aid growth and repair. It furnishes material for the purpose of the elaboration of body secretions; it supplies the organism with oxygen; and it carries away carbon dioxid and other effete material. Blood is constantly in circulation.

Blood is red, opaque, and is, in the fowl, quite viscid. The exact tint of the blood depends on whether it is drawn from an artery or from a vein. Blood from a vein has a purplish tinge while that from an artery is a bright scarlet. The color of blood is largely due to pigment in the erythrocyte, called hemoglobin.

The reaction of the blood is alkaline, due to the phosphate and the 258bicarbonate of soda. The alkalinity of the blood is reduced by work. This is due to the formation of sarcolactic acid in the muscle. The odor of blood is due to volatile fatty acids. Each kind of fowl has its own peculiar odor. The taste of the blood is saltish, due to a small amount of sodium chlorid it contains.

The blood consists of the following substances:

First, the unorganized part, or fluid, the liquor sanguinis or plasma. It contains in solution proteids, extractives, mineral matter, and gases. The gases are held in loose chemical union.

The liquor sanguinis constitutes fully 66 per cent. of the volume of the blood. It is albuminous in nature and contains a small amount of coloring matter of a fatty nature. It holds in solution three proteids—fibrinogen, serum globulin, and serum albumin.

Second, the organized parts, or the cellular structure (Fig. 74, Nos. 1 to 21). The cells float in the plasma and consist of three groups: the erythrocytes, or red blood cells, the leucocytes, or white blood cells, and the thrombocytes.

Erythrocytes.—The average number of red cells (Fig. 74, No. 21) of the domestic fowl range between 3,000,000 and 4,000,000 per cubic millimeter. The red blood cells are flattened and elliptical in shape, and possess an oval elliptical nucleus. The average length is ¹⁄₂₁₀₀ inch and the diameter ¹⁄₃₈₀₀ inch, or 7 to 8 micra in diameter and 12 to 13 micra in length. However the diameters vary in different kinds of birds. The cytoplasm is yellow and glassy, and the nucleus takes basic stains and appears somewhat picnotic.

Thrombocytes.—The thrombocyte (Fig. 74, No. 19) is of about the same length as the erythrocyte but somewhat narrower. The nucleus is round, stains purple with the Wright’s stain, and the chromatin material is somewhat diffused. The diameter of the nucleus is nearly equal to that of the cell. The cytoplasm is pale and may show vacuoles near the nucleus. They may contain small circumscribed red structures. They vary somewhat in size and shape. There are in the domestic fowl between 45,000 and 55,000 per cubic millimeter.

Leucocytes.—There are, in the blood of the hen, 28,000 to 35,000 leucocytes per cubic millimeter. The leucocytes may be divided into five distinct types. These are as follows:

Polymorphonuclear leucocytes with eosinophilic rods (Fig. 74, No. 2) are round and have a diameter about equal to the length of the erythrocyte. The nucleus is polymorphous; that is, it has two or more lobes. The nucleus stains a pale blue, and the chromatin is diffused. The cytoplasm is colorless with bright red staining spindle-shaped rods. There are 28 to 32 per cent. of this type of cell in the blood of the hen.

Fig. 74.—Blood cells of the fowl. Wright’s stain. From a S. C. Rhode Island Red cockerel. 1, Basophile (mast cell) with lilac staining spherical granules. 2, Eosinophile with rod-shaped acidophile bodies. 3 and 4, Eosinophiles with acidophile staining round granules. 5, Eosinophile ruptured. 6, Mononuclear leucocyte with vacuoles in the cytoplasm. 7 and 9, Transitional leucocytes (first stage). 8, Mononuclear leucocyte. 10, 11, and 12, Small lymphocytes. 13 and 14, Large lymphocytes. 15, A lymphocyte. 16, Lymphocyte (nucleus centrally located). 17 and 18, Transitional leucocyte. 19, Thrombocyte. 20, Neutrophile (polymorphonuclear). 21, Erythrocytes.

259Polymorphonuclear leucocytes with eosinophilic granules (Fig. 74, No. 3 and 4) are of about the same shape and size as the preceding. The nucleus is similar to the former except that it may appear slightly picnotic. The cytoplasm stains not at all or faintly blue; it contains round or spherical granules which stain a dull red. There is from 4 to 6 per cent. of this type of eosinophiles found in the domestic fowl.

Lymphocytes are round in shape and of about the diameter of the width of a thrombocyte (Fig. 74, No. 11). The nucleus is round, staining somewhat purple, and contains a diffused chromatin material. The cytoplasm exists in only small amounts; it lies to the side of the nucleus and stains a pale blue. This is the small lymphocyte. A similar cell but much larger also exists. This is the large lymphocyte (Fig. 74, No. 13). There is from 40 to 44 per cent. of the lymphocytes in the blood of the fowl. The small lymphocytes are most abundant.

Large mononuclear cells (Fig. 74, No. 6) either round or oval, in shape, whose diameter may be about that of an erythrocyte and at times much larger. The nucleus may be round, oval, or irregular, and at times rather crescent or U-shaped (Fig. 74, No. 17). The cytoplasm is abundant and completely surrounds the nucleus. The cytoplasm stains a paler blue than the nucleus. Both taking the basic stain as do the lymphocytes. These constitute 18 to 20 per cent. of the cells of the blood.

Mast cells or basophiles (Fig. 74, No. 1) are of about the same size and shape as the eosinophiles. The nucleus is round or oval, and stains a very pale blue. The cytoplasm is colorless, mostly to one side of the nucleus, and contains round or spherical purple staining granules. This type of cell constitutes from 2 to 4 per cent. of the white cells of the blood.

Structure of the Red Blood Cell.—The red blood cell is composed of a spongy stroma holding in its meshes the red coloring matter. The stroma, or framework, of the erythrocyte consists principally of nucleo-albumin; it contains lecithin, cholesterin, and salts. The red matter consists of an albuminous crystalline substance called hemoglobin, which forms about 90 per cent. of the total solid matter 260of the dried corpuscle. Each red cell offers a certain absorbing surface for oxygen. As the blood circulates through the delicate walls of the lungs and the air-sacs, it takes up oxygen; the blood at the same time delivers to the air carbon dioxid which has been brought from the tissues where active cell metabolism has been going on. This oxygen taken up by the erythrocyte forms a loose chemical union and is known as oxy-hemoglobin. In this form it is carried to the tissues of the body where it is given up by the erythrocyte to the tissues where oxidation is going on.

Hemoglobin is a crystallizable proteid substance containing carbon, hydrogen, oxygen, nitrogen, sulphur, and iron.

Formation of the Cells of the Blood.—The red blood cells are formed in the red marrow of the bone.

Polymorphonuclear leucocytes are formed in the red marrow of the bones, and the lymphocytes in the lymph glands and lymph follicles.

The bird carries a normal body temperature of 105° to 107° F. The average temperature of 50 mature hens and cocks was 106.8° F. The blood is of a deep red color.

Composition of the Blood.—The average composition of the blood of the domestic fowl as given by Owen, is as follows:

Blood when drawn and allowed to stand soon coagulates. In the blood of birds this process is very rapid, the blood coagulating, in most instances, in about one-half minute. Blood coagulates only in the presence of calcium salts.

During life, the liquor sanguinis is termed plasma; but after it has been shed from the body and coagulation has taken place, the 261liquid residue is called serum. Serum is plasma with its modifications as the result of coagulation, and as this latter process is brought about by the production of fibrin, we may say that serum is plasma minus fibrin-forming elements.

The proteids of the serum are serum globulin, serum albumin, and a ferment produced as the result of coagulation. As fibrinogen is used up in the process of coagulation, it is not found in the serum, but there is in the serum a proteid known as fibrino-globulin. This is produced from fibrinogen during the process of fibrin formation. The following tabulation gives a clear idea of the difference between the proteids of plasma and of those of serum:

Fibrinogen is the precursor of fibrin.

The fibrin of the blood clot of the bird is soft and very lacerable. The serum is usually yellow.

The power of vascular endothelium to ingest red blood corpuscles has been studied by Keys.

When bacteria or other minute foreign bodies are injected into the blood stream of pigeons, they are rapidly withdrawn from the circulation into the tissues of the liver and of the spleen. The foreign bodies are noted to be contained within cells of a distinct type, which is found in both liver and spleen. This type of cell contains, in addition to the foreign substances injected, much yellow pigment, and when tested for iron by Pearl’s method gives a positive Prussian-blue reaction.

In such specimens there is a display of contrast to other tissues. There is an extensive content of cells possessing the distinct tone of Prussian-blue iron reaction. These cells are distributed rather evenly throughout both the spleen and the liver, but more numerously in the liver.

In the liver, under low-power magnification, these cells appear as blue patches, sharply differentiated from the red-stained parenchyma. These cells are larger in their greater diameter than the liver 262cells. They vary much in size and form. They bear a constant relationship to the venous capillaries, and often appear to occupy the lumen of the vessels. Under higher magnification it is noted, however, that each cell is an integral part of the endothelial intima lining of the capillaries. They are therefore fixed tissue cells, engaged by one of its surfaces upon the reticulum of the vessel wall, with a free surface bulging a greater or less degree into the lumen of the vessel. The attached surface of the cell follows exactly the line of the vessel wall. These cells are similar to those described for mammals by Kupffer and are called Kupffer cells or stellate cells. In the fowl Keys proposes the name hemophages. The nucleus of the hemophage stains a deep garnet with the carmine used in the above-given technic, and contains two or three very distinct and intensely stained nucleoli. In the hemophages, which are more nearly flat, the nucleus appears like those of the typical endothelial cells; whereas in the protruding hemophages of greater bulk, the nucleus is more vesicular and is irregularly pyramidal in form. Rarely two nuclei are found in one cell. Within this cell may be seen vacuoles of the cytoplasm which contain red blood corpuscles. These blood corpuscles have been phagocyted from the circulating blood stream. Approximately one-third of the intimal cells are hemophages. Each hemophage displays evidence that it contains, or has recently contained, one or more red blood cells. The cell body of the hemophage has no fixed morphology, but changes from time to time according to its phase of phagocytic activity. In a stage which the hemophage has recently ingested a red blood cell, the cell body bulges out into the lumen of the vessel and the nucleus is crowded to one side. At this time the red blood cell appears as those in the blood stream and possesses the characteristic staining reactions. The nucleus of the red blood cell stains deep reddish brown and the cytoplasm an even yellow bronze. In the next stage the cytoplasm of the hemophage gives a diffuse Prussian-blue reaction. Then in hemophages which represent later stages there are various stages of disintegration and digestion of the red blood cell. The first changes of the phagocyted red blood cell is hemolysis, the hemoglobin escaping into vacuoles of the cytoplasm of the phagocytic cell, leaving the nucleus-containing stroma distinctly outlined. The stroma may retain the original ovoid form or may become spherical; the nucleus in such instances remains ovoid. Gradually, both the stroma and nucleus lose their staining reaction until finally the 263vacuoles contract about a small indistinct remnant of the nucleus, which in its turn ultimately disappears. During this latter process the size of the hemophage gradually decreases. The hemoglobin, which has escaped into the cytoplasm of the hemophage, is seen to undergo a series of changes. At first the greater part of the pigment does not give the iron reaction but retains its yellow-bronze tone with erythrosin and occupies vacuoles of various sizes. Later the contents of the vacuoles give the iron reaction and with increasing intensity. Later there is a gradual decrease in the staining reaction indicating that the iron gradually disappears from the cells which extracted it from the red blood cells it digests. As a summary we find, that these cells take care of the worn out red blood cells. They devour them; hemolyze them, destroying the stroma and nucleus; split the hemoglobin and free the iron; and then finally return to their normal form.

The spleen contains the same type cells, but they are fewer in number. For the most part they are confined to the pulp cords and have no such evident relation to the vessel wall, or lumen, as in the liver.

The function of the cells of the spleen are essentially the same as those in the liver.

Iron freed from the worn out red blood cells is not retained by the cells freeing it, nor is it found in the bile. It does not occur elsewhere in the tissues of the liver and spleen. It is possibly discharged into the blood stream, and transported to the hemapoietic tissues. Cells which hemolyze red blood cells and liberate the iron are to be seriously thought of in connection with bile formation since bilirubin is approximately, if not identical with, iron-free hematoidon.

NEUROLOGY — THE CRANIAL NERVES — THE SPINAL CORD — STRUCTURE OF THE NERVE TRUNKS AND GANGLIA — THE SPINAL NERVES — THE BRAIN — THE SYMPATHETIC NERVOUS SYSTEM — FUNCTIONS OF THE NERVOUS SYSTEM

The Nervous System.—The nervous system is an apparatus by means of which animals appreciate and become influenced by impressions from the outer world. Animals react on these impressions, and thus are enabled to adapt themselves to their environment. This system is the organic substratum of life, sensation, and motion. Broadly stated, the nervous system connects the various parts of the body with each other, and to coördinate the parts into a harmonious whole in order to carry on the bodily functions methodically and to control the physiological division of labor throughout the organism.

The nervous system consists of two parts. The first is the cerebro-spinal system, which comprises the central nervous axis, including the brain and the spinal cord, and the peripheral nerves, including the cranial and the spinal nerves. The second is the sympathetic nervous system. The two parts of the system are closely linked together, and both terminate in peripheral nerve endings, including those of special sense, of sensation, and of motion.

The cerebro-spinal nerves especially preside over the special senses, motion and sensation; and the sympathetic over the digestive, the pulmonary, and the vascular apparatus.

From a structural standpoint, the nerve system consists of cell elements peculiarly differentiated from all other tissue cells in that their protoplasm is extended in the form of processes, often to great distances from the nuclear region. The cell elements are held in place by supporting tissue and receive an abundant blood supply; they are partly of ectodermal and partly of mesodermal origin.

The cell element of the nerve system, called a neurone, is the developmental, structural, and functional unit of the nervous system. It is a single cell presenting unusual structural modifications. It comprises not only the nerve cell body with its numerous protoplasmic processes, or dendrites, but also the axone, which may vary in length from a fraction of a millimeter to fully half the bird’s length. The bulk of the axone is many times the bulk of the cell body.

265Certain non-medullated axones are surrounded by a delicate, homogeneous, nucleated sheath, called the neurilemma, or sheath of Schwann.

The cranial nerves have their origin in the brain and leave the cranial cavity in pairs. They are numbered numerically from before backward, there being twelve pairs in all. The following is a tabulation according to their number, name, and function:

Olfactorius.—Nervus olfactorius (Fig. 75, C, 16). This is the nerve of smell, one of the nerves of special sense. The organ of smell consists of five layers as follows:

First, a layer of olfactory fibers extending in different directions and consisting of a dense plexiform arrangement of the axones of the olfactory cells. From this layer the fibers pass into the layer of olfactory glomeruli where their terminal ramifications mingle with the dendritic terminals of cells lying in the more dorsal layers, to form distinctly outlined spheroidal or oval nerve fiber nests, the olfactory glomeruli.

Second, a fine granular layer of basic substance containing round cellular structures, the stratum granulosum.

Third, broader granular, or molecular layer, having on its inner surface a row of large pyramidal cells which are both small and large and which send their dendrites into the olfactory glomeruli. Their points are directed outward.

Fourth, a layer of round cells tightly pressed together and measuring about 5 microns in diameter. Between these cells are very fine nerve fibers.

266

Fig. 75.—The brain of a hen. Photograph.

A. Upper surface of the brain. 1, Medulla oblongata. 2, Calamus scriptorius. 3, Cerebellum. 4, Optic lobes. 5, Transverse fissure. 6, Longitudinal fissure. 7, Upper surface of the left cerebral lobe. 8, Upper surface of the right cerebral lobe. 9, Lateral pillar of the cerebellum.

B. The posterior surface of the eyeball. 10, The sectioned surface of the optic nerve.

C. The inferior surface of the brain. 11, Corneo-scleral juncture. 12, The cornea. 13, The sclera. 14, The optic nerve. 15, The optic chiasm. 16, The olfactory lobes. 17, The medulla oblongata. 18, Tuber cinererum et infundibulum.

267Fifth, a layer of epithelial cells.

The peripheral fibers and the nerve cell layers near the hemispheres disappear so that the basic substance of the trabecula with the hemispheres form the entire lobe mass. On the lower surface of the hemispheres there is a long bundle of nerve fibers which enter into the substance of the olfactory lobes and there disappears. These fibers are medullated. Non-medullated fibers enter into the makeup of the olfactory trunk.

The original center of the olfactory nerve is not in the hemisphere, but in the same location as the optic nerve. This nerve trunk consists of very fine non-medullated fibers. The nerves of smell are therefore not peripheralistic nerves. The nerve fibers are distributed to the mucous surface of the turbinated bones. Toward the front they form an expanded prolongation.

The olfactory nerve, as it emerges from the cone-like anterior tip of the cerebrum, is of considerable thickness and extends along with the median dorsal artery of that region above and to the inside of the orbit, under the thin bony structure. Before its termination into the posterior turbinated bones, it is crossed by the superior maxillary division of the fifth pair of cranial nerves. It extends as far as the pituitary membrane of the turbinate bones upon which its filaments are distributed radially.

The Opticus.—The nervus opticus (Fig. 75, No. C, 14) the second cranial, is the nerve of sight. The optic lobe, or tuberculum bigeminum lies at the base of the brain on each side of the optic tract.

From the optic lobes the two trunks pass forward along the under surface of the cerebri, forming the optic chiasm at the hypophysis (Fig. 75, No. C, 15), at which point the nerve fibers originating from the right side pass to the left, and vice versǎ. From the chiasm the true optic nerves pass forward to the posterior surface of the eyeball. They are composed of a bundle of very fine, marrow-like nerves. These fibers enter into the ganglionic cells of the retina. By removal of the finely adherent neurilemma, the optic nerve is seen to be composed of parallel, longitudinal lamellæ, the margins of which are mostly free on one side.

The Motor Oculi.—The motor oculi (Fig. 62, No. C, 10), the third cranial nerve is a motor nerve. It originates close to the base of the brain behind the position of the hippocampus of mammals on the inner side of the crus cerebri, and also on the inner 268somatic column close below and somewhat aside from the aqueduct of Sylvius. The nerve leaves the brain cavity through a distinct foramen near the foramen opticum, and supplies the following eye muscles: first, after entering the orbit, it sends a branch upward to the inferior portion of the inferior rectus; then, it gives off the thick ramus ciliaris. The trunk then extends under the optic nerve and passes forward to innervate the inferior rectus, the internal rectus, and the inferior oblique. A ciliary ganglion forms on the trunk.

The Patheticus.—(Fig. 62, No. C, 11) is a small motor nerve, originating close to the sulcus centralis, in the circle of the center brain over the valve of Vieussens, between the posteriors of the optic lobes. It extends in a dorsal direction between the cerebellum and the lobus opticus, to the posterior of the latter of which it then forms a loop ventrally. Lying close to the optic foramen it passes through a fine opening into the eye cavity and supplies the superior oblique muscle of the eye. During its course it passes dorsally over the optic nerve, and then crosses dorsally over the ophthalmic division of the fifth pair of cranial nerves and the internal rectus muscle.

The Trifacialis.—(Fig. 62, No. C, 12). This, the fifth cranial, is a mixed nerve and is divided into two parts, portio major and portio minor.

The portio major originates in the ganglion cells of the posterior part of the brain. Commencing near the medulla oblongata it passes through the posterior part of the brain, then upward and outward; and along its route it forms the Gasserian ganglion, which lies partly in the cranial cavity or in its wall.

The portio minor consists of the downward passing fibers containing the motoric elements which are distributed to the muscles of the jaw and of the eye. The roots are found in the ganglion from the center and back brain, close below the pathetic nerve origin, where the pathetic passes between the lobus opticus and the pars peduncularis; it then takes a lateral course between the two.

The fibers of the portio minor do not take part in the formation of the Gasserian ganglion, but are only partly surrounded by it.

There are three nerve trunks given off of the trifacialis: the ophthalmic, the superior maxillary, and the inferior maxillary.

The ophthalmic division of the fifth nerve is the smallest of the three branches. It emerges directly from the Gasserian ganglion, 269and passes through a narrow bony canal in the base of the brain, below the pathetic and the abducens, and through the foramen ophthalmicum. It then enters the eye cavity above the optic nerve, and on the wall of the cavity extends downward, and with regard to the eyeball, dorsally lying close to the rectus internus muscle and close to the surface of the eyeball. It passes along the olfactory nerve, extends under the superior oblique muscle, and finally reaches the inner angle, or canthus, of the eye. It here divides into the recurrent externa and the ethmoidalis. The ethmoidalis branch is a straight continuation of the ophthalmic. It extends along close to its fellow of the opposite side, and, over the vomer, splits into two branches. The smaller of these branches breaks through the bone cells of the jaw, continues upon its ventral surface in a furrow extending forward, and terminates in the gum region. It supplies the gum and point of the beak. The larger branch enters into the cell substance extending to the tip of the beak, in its course sending out a number of fine filaments, which spread out along the outer surface. At this point these two branches may fuse. The larger branch is endowed with the sense of touch.

The recurrent externa divides shortly after leaving the main trunk of the eye cavity passes over the lacrimal gland. It gives two branches to this gland and one to the membrana nictitans, and innervates the upper eyelid. It then emerges from the eye cavity, passing over the os lacrimale, and gives one or more branches to the integument of this region, including the comb. This branch is large in birds with a large comb. Branches pass in front of the lacrimal bone through the outer nasal cavity and into its deeper structure.

Shortly after the ophthalmic branch has entered into the eye cavity and before it crosses the optic nerve, it gives a fine branch to the motor occuli.

The second and the third branches of the fifth cranial nerve are mixed. They contain elements of both the portio major and the portio minor. These two branches come from the lower part of the outer region of the ganglion, and pass together through a cavity which is located between the os petrosum and alæ and basis sphenoid, and then branch.

The ramus secundus, or superior maxillary division, of the trifacial, is the second branch and passes into the orbit below the optic nerve and the eyeball. It is called the recurrent infra-orbitale. 270It gives an ascending branch to the gland of Harder, one to the conjunctiva, one to the membrana nictitans, and one to the eyelids. It also gives a branch to the skin below the eye and to the angle of the mouth. This latter branch is called the recurrent subcutaneous. These two branches communicate with the recurrent nasal ciliaris of the first trigeminus branch. The second branch passes below the nasal opening, then passes on and forms the alveolar nerve on the side between the gums. It sends several recurrent posterior branches to the elevations on the back part of the mouth. It extends forward to the point of the beak.

The inferior maxillary division of the fifth is larger than the other two. It is directed downward and outward then upward to the temporal region. At the temporal region it divides into five parts. It gives a branch to the temporalis muscle, one to the pterygoid muscle, and one to the mylo-hyoideus. The main branch gives twigs to the parotid gland region and enters into the dental canal of the lower jaw. Numerous filaments break through the lower jaw bone, and then spread out on the skin and rim of that bone. The largest branch, called the recurrent maxillaris externa, comes out near the coronoid process. The rest of the trunk extends to, and comes out of, several foramina at the anterior point of the jaw bone.

These filaments are contained in grooves or cavities of the lower jaw and terminate in touch buds.

The trifacialis fuses with the other cranial nerves and with the sympathetic nervous system. Some of these fusions are as follows: The recurrent ophthalmica fuses with the orbito-nasalis ganglion. Indirect fusion of the recurrent maxillary division of this nerve takes place near the Gasserian ganglion through the sympathetic nerves, the temporo-lacrimalis, the facial nerves, the large cervical ganglion, and indirectly with the glosso-pharyngeal and the vagus. This fusion has been called the superior recurrent branch of the trigeminus, or trifacialis.

There is a direct fusion of the superior recurrent maxillary division of the fifth just before entering the upper jaw. This fusion is with the spheno-palatine ganglion and the sympathetic carotidis cephalica, and also with the large cervical ganglion.

The Abducens (Fig. 62, No. C, 13).—This nerve originates in the somatic and motoric column along with the other nerves of the eye muscles. Its nucleus lies in the circle of the pars commissuralis of 271the cerebellum. The nerve then passes ventrally, as does the motoris oculi and leaves the brain along the median line. This is a comparatively large nerve and passes somewhat laterally and ventrally from the foramen opticum through a canal in the sphenoid. It then enters the orbital cavity. Some muscular twigs are given off to the quadratus and to the pyramidalis muscle. This nerve also innervates the external rectus muscle of the eye. The abducens anastomoses with the ramus ciliaris and the ophthalmic nerve and gives fine nerve twigs to the ramus ciliaris externus of the ciliary ganglion.

The Facialis and the Acusticus.—The facial nerve originates with the auditory (Fig. 62, No. C, 14 and 15) in a very vaguely known manner, from the cerebellum. It divides into three parts.

The first of these probably comes from the complex ganglion with the posterior roots of the auditory. This part belongs to the somatic sensory group of nerves. From this same group originates the auditory, which spreads out into the cochlea and takes the impressions of sound. This nerve is short and thick, and, at the point where it loses its medullary covering on entering the cochlea, there is developed a ganglion. This ganglion is similar to the spinal ganglia.

The second part is provided with one root which originates mesially and ventrally, from the deeper ganglion cells. Some of the fibers from this root constitute the vestibular branches. They accompany the auditory and supply the anterior part of the ear labyrinth and the semicircular canals. The larger part of the fibers of this trunk make up the intermediate part of the facial. The geniculate ganglion is formed at their fusion. The sympathetic spheno-palatine nerve emerges from this ganglion, coming out of the aqueduct of Fallopius.

The third part, called the portio dura, is the main facialis. It is located opposite the auditoria intermedia. Its roots may be traced to the complex ganglion, from which they take a direction ventrally from the median portion.

The facialis, after emerging from the aqueduct of Fallopius, takes a curved course and partly fuses with the sympathetic temporo-lacrimalis on the upper posterior wall of the ear drum. It is here accompanied by the carotid and the cephalic arteries. It leaves the ear drum through an opening in the quadrate bone, giving off a large branch to the digastricus muscle and a small one to the stapedius of the columella auris. The facialis trunk is quite large. It 272then passes downward along the quadrate bone, where it receives a large branch from the glosso-pharyngeus. This nerve also gives branches to the mylo-hyoideus and the stylo-hyoideus muscle, crosses laterally the glosso-pharyngeus, and finally fuses with branches of the subcutaneous and with the first, the second, the third, and the fourth cervical nerves. After this fusion the nerves innervate the skin of the anterior of the neck and the constrictor colli muscle.

The facialis anastomoses as follows: with a fine branch of the sympathetic temporo-lacrimalis, indirectly with the ramus trigeminus, with the large cervical nerve ganglion and with the spheno-palatine ganglion and nerve.

The Vagus Group.—The ninth, the tenth, and the eleventh cranial nerves are by some anatomists called the vagus group, first so called by Willis. They are made up of both sensory and motor nerves.

The Glosso-pharyngeus.—The roots of the glosso-pharyngeus (Fig. 62, No. C, 16; Fig. 76, No. 13) emerge, along with those of the vagus, from the medulla oblongata, and enter, as a short trunk, the foramen jugulare et caroticum. Between these two nerves there is usually found a thin portion of bone. The trunk of the glosso-pharyngeus forms a ganglion in the foramen jugulare et caroticum where it receives connecting branches from the near-by ganglion radicis and vagus nerve. The glosso-pharyngeus passes out of the foramen jugulare et caroticum above the large superior sympathetic nerve ganglion, with which it communicates. The glosso-pharyngeus passes diagonally over the ramus temporo-lacrimalis of the sympathetic system, and then receives a very strong branch from the vagus (Fig. 76, No. 12). It sends a short branch to the recurrent lacrimalis of the sympathetic system. At this point there is formed a reddish-yellow ganglion, the petrosal ganglion, which is similar to the petrosal ganglion of mammals. Frequently it is found close below the large superior cervical nerve ganglion. The petrosal ganglion is frequently connected by special fibers with the cervical nerve ganglion, the large superior cervical nerve ganglion and the ganglion radicis vagi. The glosso-pharyngeus is divided into the following branches.

First, the recurrent pharyngeus which gives branches to the upper part of the throat and which is tortuous in its course. It receives a branch from the superior cervical nerve ganglion and gives off branches to the salivary glands and papillæ of the posterior tongue region.

273Second, the recurrent lingualis, which passes with the lingual artery over the hyoid bone to the base of the tongue and to the papillæ. Another branch passes below the tongue bone and supplies the tongue and the pharynx. The glosso-pharyngeal is a mixed nerve.

Fig. 76.—Photograph of spinal cord of a hen. 1, Cerebrum. 2, The olfactory nerve terminating at 3, the turbinated bones. 4, The superior maxillary division of the fifth nerve dividing. 5, The eye with the upper part laid open. 6, The cervical segment. 7, The lumbo-sacral segment. 8, The lungs. 9, The kidneys lying above the peritoneum. 10, The terminal filament of the spinal cord. 11, The hypoglossal nerve. 12, The vagus nerve. 13, The glosso-pharyngeal nerve. 14, The branch from the vagus.

The Vagus.—The vagus, or pneumogastricus (Fig. 18, No. 5; Fig. 62, No. C, 17; Fig. 76, No. 12), a mixed nerve, forms a ganglion 274in the foramen through which it passes. The foramen lies between the os petrosum and os occipitale, close to the foramen jugulare, above and to the inside of it.

The ganglionic root of the vagus communicates with the superior cervical nerve ganglion. The vagus, after coming out of the foramen, takes up branches of the spinal accessory, passes to the superior nerve ganglion, crosses the carotid artery, and then, accompanied by the internal jugular, it connects by a branch with the hypoglossal. It then communicates with the petrosal ganglion, and receives a long branch from the superior cervical ganglion. It then extends along the neck with the jugular vein and often fuses with the sympathetic ganglionic plexuses. As it passes, it is interwoven with the glosso-pharyngeus, but each nerve element retains its own individuality. Extending down the neck, on entering the thoracic cavity, it lies between the plexus brachialis and the carotid artery. Then it passes below the subclavian artery, and between the bronchial tubes, the aorta pulmonalis, and the subclavian vein. Then ventrally it rests upon the glands, and the right and the left vagi fuse or unite. From here they radiate down to the stomach in fan-shape, and, continuing, they fuse with the sympathetic system.

The other branches of the vagus are:

The first branch is the recurrent laryngeus, which supplies the lower end of the bronchial tubes, and the esophagus, then enters above the bronchus near the origin of the subclavian artery as the recurrent cardiacus.

The second are the recurrent pulmonale which pass into the lungs, each fusing with its fellow from the opposite side, and giving off branches inferior to the vena cava including a branch to the heart.

The third are the recurrent hepatici which pass through the diaphragm and are distributed to the liver.

The Accessorius Spinalis.—This is a very small motor nerve (Fig. 62, No. C, 18). It comes out between the dorsal and the ventral root of the third cervical nerve. It lies close to the neck and extends anteriorly, receiving roots from the first and the second cervical nerve. It passes through the occipital foramen into the brain cavity and then enters the ganglion radicis vagi. It passes out of the cranial cavity through the foramen jugulare. It then partly fuses with the vagus and partly, as a fine branch, with the subcutaneous colli.

The Hypoglossus.—The hypoglossus is a motor nerve (Fig. 62, No. C, 19). It originates anterior to the eleventh pair of cranial 275nerves, and from the same ganglion as the abducens and the motor oculi. It leaves the medulla oblongata from its ventral surface, and passes with a posterior and an anterior branch out of the cranial cavity through two separate foramina in the os occipitale laterale. The posterior branch, much smaller than the anterior, passes between the cranial bones and the cervical sympathetic nerve; it then passes at right angles through the rectus capitis anticus, and, while closely following the carotid artery, it fuses with the anterior branch. The larger, anterior branch, much stronger than the posterior, sends a short strong branch to the complexus muscle. The rest of this branch, which probably has sympathetic elements, is disposed as is a spinal nerve. It crosses the sympathetic nerve, and at this point forms a typical cervical sympathetic ganglion. It also forms a short loop with the recurrent ventralis of the first cervical plexus. From this loop, after it has given off several branches to the muscles of the neck, it gives off one or two strong branches, which fuse with each other and with the posterior thin branch, thus forming the trunk of the hypoglossus. It receives many elements from the first cervical nerves.

The hypoglossus sometimes communicates with the vagus, crosses over the latter, and divides itself into two main branches, as follows:

First, the recurrent laryngo-lingualis, which passes between the cornua of the os hyoideum and the larynx to the anterior part, and furnishes the principal tongue muscles. It extends along the inferior surface of the tongue and fuses with the one of the other side and extends to the free tip of the tongue. This nerve probably receives sensory elements from the second root and from the confluent of the first cervical nerve. This form of anastomosis is well marked in birds with thick tongues, as ducks.

Second, the recurrent laryngeus furnishes the muscles of the superior larynx and of the tongue skeleton. It extends downward and also furnishes the muscles of the trachea. It follows the course of the jugular vein and at the entrance of the chest supplies the furcula. The nerve passes into the thorax, downward along the side of the bronchial tubes, and supplies innervation to all the muscles of the inferior larynx.

Structure of the Cord.—The spinal cord is called the myelon or medulla spinalis. It is a comparatively large, white, irregularly 276cylindrical cord, flattened from above downward. It extends from the foramen magnum at the base of the medulla to the caudal portion of the spinal canal where it terminates in a fine filament. In order to allow considerable motion of the spinal column without danger of injury to the spinal cord, the cord is loosely suspended in the canal. The meninges, or coverings, are continued from the brain. In addition to these there are to be found arteries, veins, and nerves entering and others making their exit from the canal and from the cord. At the cervico-dorsal juncture, where the brachial plexus is given off, the cord is enlarged. There is another enlargement at the point where the lumbo-sacral plexus is given off. At this point, superiorly, there is a longitudinal cavity called the sinus rhomboidalis. This sinus contains a gelatinous substance. There is a pair of nerves given off at each intervertebral foramen. Thus there are as many pairs of spinal nerves as there are vertebral segments. The inferior root is the motor root and carries the impulses from the cord to the periphery. The superior root is the sensory branch and carries the impulses from the periphery to the cord, and thence the impulse is carried to the centers in the brain. The sensory and the motor roots are of about equal size. The inferior have more numerous filaments. The ganglion on the superior or sensory root is relatively large. In the sacral region the sensory and the motor branches pass through their own bony canal.

White rami communicantes are given off at each intervertebral foramen to the sympathetic system and gray rami are received from the sympathetic ganglia. Thus there is established a direct communication between the sympathetic and the spinal system. There is a ganglion on the superior root just outside the spinal cord.

The ganglionic portion, or gray matter, is arranged in the center of the cord in two comma-shaped parts forming an X. The white matter, or the material forming the fibers, is arranged around the central ganglionic portion.

The spinal cord may be divided into two lateral symmetrical halves. There are two longitudinal fissures, one on the upper and the other on the lower half. The upper called the superior median fissure is narrow but deep. The one on the inferior side, called the inferior median, is usually more pronounced. The superior parts of the gray matter are called the superior cornua, or horns; the inferior parts the inferior cornua, or horns. The center of the cord 277is pierced by a central canal which communicates with the fourth ventricle at the calamus scriptorius.

The protoplasmic processes called dendrites have a similar structure to the cell body. The dendrites branch dichotomously, become rapidly smaller, and usually end at no great distance from the cell body.

The axone or axis cylinder process, differs from the cell body and from the dendrites. It does not contain chromophilic granules. It consists entirely of neurofibrils and perifibrillar substance. It emerges from the cell at an enlargement known as the axone hill. This hill is free from chromophilic bodies.

Nerves are divided into two kinds, medullated and non-medullated.

Medullated nerves are divided into two kinds: medullated nerves with a neurolemma, and medullated nerves without a neurolemma.

Medullated nerves with a neurolemma consists of an axone, a medullary sheath, and a neurolemma. A delicate membrane called an axolemma, or periaxial sheath envelops the axone. The medullary sheath called myelin, is semifluid, somewhat resembling fat. The outer covering is the neurolemma, or sheath of Schwann. It is a delicate, structureless membrane which incloses the myelin. There is under this sheath an occasional oval nucleus. At intervals there are constrictions, or nodes, called the constrictions of Ranvier. The part between the nodes is called the internode.

The medullated axones without a neurolemma are the medullated nerve fibers of the central nervous system.

The non-medullated axones, or non-medullated nerve fibers, are divided into non-medullated axones with and those without, a neurolemma.

The non-medullated axone without a neurolemma is merely a naked axone. They are confined to the gray matter and to the beginnings and endings of sheath axones, all the latter being uncovered for a short distance after leaving the nerve cell body and also just before reaching their terminations.

The long axones serve to make connections with the peripheral, or distant, nerve cell, muscle cell, or gland cell; while the shorter axones of certain neurones divide into terminal branches in the immediate vicinity of its cell body, presumably to come into relation with other nerve cells in the same or adjacent groups.

278

Fig. 77.—Histological structure of tissues.

1. Non-striated or involuntary muscle cell. a. 1, Nucleus; 2, Protoplasm. b. Transverse section showing nuclei in the center of the cells that are cut through the nuclear zone. c. A cross-section of the connective tissue which binds together the muscle cells. d. A section showing the so-called intercellular bridges.

2. A cross-section of the rectus abdominalis. 1, The endomysium which binds the cells into primary fasciculi or bundles. 2, The perimysium which surround the bundles of fasciculi. 3, The epimysium which surrounds the muscle. These binding structures are white fibrous connective tissue.

3. A longitudinal section at the juncture of a muscle and tendon. a, The279 juncture between the muscle and tendon. Note the many nuclei in both muscle and tendon. This is voluntary or striated muscle which make up the dermal, dermo-osseous and skeletal muscles.

4. A longitudinal section of heart muscle. a, Connective-tissue cell. b, Nucleus of a muscle cell. c, Cement line between the muscle discs. d, The cell or segment.

5. A bipolar ganglionic nerve cell. a, The nucleus. b, The nucleolus. c, The fibrillar structure. d, The medullary sheath.

6. A diagram showing the scheme of the peripheral nerve trunk. a, The neuraxis of the peripheral sensory neurone. b, The spinal ganglion of the superior or sensory root. c, The dendrite or peripheral nerve fiber of the sensory nerve. d, The nerve trunk. f, The sympathetic nerve ganglion connected with the spinal cord through the white and the gray ramus communicans. e, The neuraxis of the sympathetic neurone. g, Neuraxis or trunk of the motor neurone or nerve cell. h, The anterior horn of the gray matter of the spinal cord.

7. A diagram of a peripheral sensory neurone. a, The neuraxis which ends in the spinal cord or brain. b, The T-shaped division of Ranvier. c, The dendrite or sensory nerve fiber in the nerve trunk. d, The nucleus and nucleolus of the cell e., f. the axis cylinder process of the cell. g, The telodendrions or terminal branches of the dendrite or axis cylinder.

8. A schematic diagram of the sensory motor reflex. a, The telodendria. b, The dendrite. c, Nerve cell of the motor neurone. d, The motor neurone. f, The muscle fiber. g, The neuraxis of both sensory and motor neurones, the upper being the sensory. h, The nerve cell in the sensory ganglion. i, The sensory neurone or axis cylinder (nerve fiber). j, The skin with peripheral telodendrion of sensory neurone.

Neurones are devoted to the maintenance of functions. Reproductive neurones are so arranged as to receive afferent nerve impulses from other tissues; emissive neurones give off efferent nerve impulses. The former are sensory neurones; the latter are motor neurones if connected with muscles, and excito-glandular if connected with gland cells. The basis, then, of the nerve system is a series of neurones, with projecting and association processes, coördinated for the purpose of performing specific actions manifested either by motion, by trophic changes, or by the apperception of stimuli of a chemic, mechanic (tactile and auditory), thermal, or photic nature.

The whole of the nerve structure is composed of the nerve tissue and supporting connective tissue. The neurones constitute the nerve tissue, while the supportive tissue is composed of neuroglia and of white fibrous tissue derived either from the investing membrane or from the sheaths of its numerous vascular channels.

The neurones, or nerve cells, exhibit marked variations as to external characters, dimensions, and form. The neurone presents a swollen cell mass and a nucleus; it is known as the ganglion cell. From this cell body are given off a number of processes of two distinct kinds: first, protoplasmic processes, which are commonly branched, called dendrites; second, a single, thinner, and paler process; the axis cylinder process.

280The bodies of cells vary in size from 4 to 100 microns or more in diameter. The largest cells occur in the inferior horn of the spinal cord, in the spinal ganglia, in the large pyramidal cell layer of the cerebral cortex, in the Purkinjean cell layer of the cerebellum, and in Clark’s column of the spinal cord. Very small cells occur in the olfactory bulbs, in the granular layer of the cerebral and cerebellar cortex, and in the gliosum cornuale of the cord.

Nerve cells are classified according to the number of processes arising from the cell body, and neurones are referred to as unipolar, bipolar, and multipolar.

Unipolar cells are met with frequently in early stages of embryonic development, but are rare in adults, occurring only in the retina, in the olfactory bulb, and within the baskets of the Purkinjean cells of the cerebellum. The cells of the cerebro-spinal ganglia, except the cochlear and vestibular, are apparently unipolar, but they are developmentally and functionally of bipolar nature.

Bipolar cells are found almost exclusively in the peripheral sensory system, as in the olfactory membrane, in the retina, in the cochlear and vestibular ganglia, and in the cerebro-spinal ganglia of the embryo.

Multipolar cells are the most numerous and form the principal elements of nerve centers throughout the system. They are termed multipolar because of the greater or lesser number of dendrites given off in addition to the single axone.

The body of the nerve cell consists of a mass of protoplasm surrounding a nucleus. The cytoplasm of the nerve cell consists of two distinct substances: first, neurofibrils; second, perifibrillar substance. In most nerve cells there is a third substance called chromophilic bodies.

The neurofibrils, extremely delicate, are continuous throughout the cell body and all of its processes. Within the body of the cell they cross and interlace and probably anastomose.

The perifibrillar substance is a fluid or a semifluid substance which both in the cell body and in the processes surrounds and separates the neurofibrils.

The chromophilic bodies are granules or groups of granules which occur in the cytoplasm of all the larger and of many of the smaller nerve cells.

The first pair of spinal nerves come out between the atlas and the occipital bone. Each nerve divides into three branches. The first is the anterior branch which innervates the dorsalis, the biventer cervicis, the cervicales, and the caput posticus muscles. The second is the recurrent ventralis which passes mesially and downward from the recurrent communicans. It innervates the rectus capitis anticus muscle and joins a branch of the hypoglossal nerve. There is given off a white ramus communicans to the sympathetic nerve.

The second spinal nerve emerges from the opening between the first and the second cervical vertebræ and is similarly disposed as the first cervical. It gives off a branch called the recurrent ventralis which fuses with branches of the first cervical and the hypoglossal nerve. This nerve innervates the complexus muscle.

The succeeding cervical nerves emerge in a similar manner down the neck and are distributed to the muscles and other structures of the cervical region. The second, the third, and the fourth cervical nerve gives off branches which form anastomosing loops with the facial nerve.

According to Gadow the last cervical nerve passes between the last cervical and the first dorsal segment. There are thus fifteen pair of cervical nerves.

The first pair of dorsal nerves pass out between the first two dorsal vertebræ. The first few dorsal nerve branches innervate only the trunk muscles. Other branches supply the skin and the other adjacent integument. The ventral branches of the cervical nerves often communicate with the ventral branches of the first dorsal nerves. These branches are larger than the superior branches and aid in the formation of the brachial plexus. Smaller inferior branches are distributed to the scalenus and other muscles, and extend as far posterior as the intestines.

The dorsal branches of the spinal nerves in the lumbo-sacral region are very small, on account of the lack of extensive development of the muscles of this region. The elements entering into these nerve trunks are largely vasomotor nerves. In addition to the upper twigs supplying the skin and the other integument of the region, other branches descend into the abdominal cavity.

The caudal spinal nerves are not well developed and disappear in the region of the caudal vertebræ. The dorsal branches innervate 282the levator muscles, and the ventral branches the depressor muscles.

There is thus given off, throughout the vertebral column, a pair of nerves between each two vertebral segments, making as many pairs of nerves for the region as there are vertebral segments of that region.

The Brachial Plexus.—The brachial plexus (Fig. 73, No. 19) arises principally from the roots of the last three cervical and the first dorsal spinal nerves. These branches anastomose beneath the deep face of the scapulo-humeral articulation.

The brachial plexus divides into two distinct parts. The first (Fig. 73, No. 20) the dorsal called the superior thoracic is distributed to the serratus and the rhomboideus muscle. The second is the inferior thoracic (Fig. 73, No. 21), which consists of the main plexus, and which gives off muscular branches especially to the sterno-coracoideus and to the main portion passing on as the nerve trunk to the structures of the wing.

From the superior thoracic plexus there are several secondary plexuses formed.

The dorsalis or serratus plexus. This plexus is located adjacent to the anterior part of the main plexus and is formed of from two to four spinal nerve branches. The rhomboideus is supplied by branches which may be traced to the first root of this plexus. This nerve is called the rhomboideus superficialis. Another nerve is given off from the middle part of the dorsal side of the plexus and is called the rhomboideus profundus. A third, the superficialis serratus, is the largest of the branches. It breaks up into terminal branches, one going to each serration, or digitation, of the serratus muscle. Branches from the anterior portion of this plexus are distributed to the patagii muscles.

The superior brachial plexus gives off the following nerves:

The subcoraco-scapularis, which is purely a motor nerve, springs from the anterior roots of the plexus. It gives off a branch to the following three muscles: subcoracoideus, subcoracoido-scapularis, and scapulo-humeralis.

The scapulo-humeralis is distributed to the scapular humeral region.

The latissimus dorsi is located on the peripheral border of the scapulo-humeralis or supraspinatus. It originates from the second, and the fourth nerve roots of the plexus. It is located on the dorsal 283side of the plexus. It divides into two main branches, one going to the latissimus dorsi and the other to the scapulo-humeralis muscle. From the side are given off branches which supply the patagii muscle and enter into the formation of the dorso-cutaneous plexus.

The axillaris springs from the second and the third root of the brachial plexus, extends in a lateral direction, passing the ventral and distal rim of the insertional part of the posterior scapulo-humeralis or teres et infraspinatus and enters near the capsular ligament of the shoulder-joint. It gives off to this joint a small branch, called the recurrent articularis, which passes outward between the triceps brachialis and the humerus. It lies on the inner side of the major deltoid, and patagii muscles, and also the skin of the lateral shoulder and the upper arm region. The recurrent axillaris communicates with the main branch of the radial nerve.

The cutaneus brachii superior is a small nerve which springs from the last brachial plexus root and passes between the skin and the triceps brachii muscle on the dorsal surface of the upper arm, or brachial, region. It extends down over the elbow region, where it gives off numerous branches to the skin of these regions, to the meta-patagium and to the extensor muscles of the upper arm.

The brachialis longus superior is a large nerve trunk which springs from most of the other plexus roots. It extends around to the dorsal side of the upper arm and supplies the skin, the feathers, and the muscles of the forearm and the hand. Branches from this nerve trunk supply the triceps brachii and other muscles of the region. The main branch passes between the radius and the ulna, and, passing the elbow-joint, gives off branches to that joint. Passing on, it divides into two branches. One of these extends superficially over the upper part of the condylus ulnaris and supplies the extensor digitorum communis and the extensor metacarpi ulnaris, or flexor metacarpi radialis muscles, and, continuing superficially to the ulnar side, is distributed to the skin of the region. The second, a deep branch, extends on the ulnar side of the radius over the extensor indicis longus, and innervates the latter muscle, the extensor pollicis longus, the extensor pollicis brevis, the adductor pollicis, the interosseous palmaris, and the flexor digitorum.

The inferior brachial plexus gives off the following branches:

The supra-coracoideus, a large nerve which springs from the 284first main root of the plexus, and passes outward through the foramen coracoideum of the sternal ligament.

The sterno-coracoideus, a small nerve which extends downward from the plexus.

The somewhat large posterior coraco-brachialis, nerve which springs from one or two middle roots of the plexus and accompanies the pectoral nerve.

The anterior thoracic, a large nerve which springs from two or three of the posterior roots of the plexus and extends to the shoulder cavity where it branches. The anterior branch is distributed to the patagium and the front part of the pectoral muscles. The posterior branch supplies muscles along the side of the thorax and extends into the abdominal muscles.

The anterior coraco-brachialis, a small nerve which springs mostly from the inferior longus brachialis, passes to the distal end of the tuberculum humeralis radii, then passes backward between the front part of the humerus and the biceps, where it supplies the anterior coraco-brachialis.

The cutaneous brachialis et inferior brachialis, a small nerve which springs from the posterior roots of the plexus. It is distributed to the skin of the region and branches are given off to the patagii and the ventral wing surface. A few branches extend as far as the upper arm.

The brachialis longus inferior (Fig. 68, No. 2), a continuation of the main trunk of the inferior brachial nerve, which comes out of all the plexus roots except the first. It gives off some branches to the pectoral region and then enters the shoulder cavity. It gives off the anterior coraco-brachialis, passes down the humerus in an S-shape, and divides into two branches, the ulnar and the median.

The ulnar nerve (Fig. 67, No. 3) divides into numerous branches which are distributed to the ulnar side of the forearm and the hand. The ulnar nerve passes below the skin of the ulnar outside rim of the forearm and gives branches to the carpi ulnaris, finally supplying the flexor digitorum; it then passes with the tendon of this muscle downward to the interosseous dorsalis, the abductor indicis, or flexor minimi brevis, the flexor pollicis, and the abductor pollicis, or extensor proprius pollicis.

The median nerve (Fig. 67, No. 2) extends down the arm and gives branches to the biceps muscle, and to the patagii region. Continuing, the median nerve supplies the pronator muscle and the brachialis 285inferior, or brachialis anticus, and then divides into two branches. The first and largest branch passes between the two pronator muscles giving branches to the pronator profundus, or pronator longus, and the flexor digitorum profundus muscle. This nerve then passes anteriorly along the tendon to the base of the digit, and, on the dorsal side, joins the other branch of the median nerve. At this point there is often a plexus, and at the point of fusion of the ulnar nerve on the ulnar side there may also be a small plexus. These plexuses mainly supply the skin of these regions. The second branch, passes forward, crosses the extensor carpi radialis and lies just below the pronator profundus, or pronator longus, giving branches to the skin. It passes downward on the radial side of the ulnar and supplies the muscles of that part; it then continues down the hand. Branches are given off to the extensor proprius pollicis, the interosseous dorsalis, the flexor digitorum, and to the skin between the thumb and the forefinger.

The intercostal nerves (Fig. 70, No. 18) are given off from the spinal cord of the dorsal region. The superior branches are small and supply the superior dorsal region. The inferior branches lie one behind each rib, innervate the intercostal muscles, and give a few twigs to the superficial thoracic muscles.

The Lumbo-sacral, or Crural, Nerve Plexus.—The crural plexus (Fig. 70, No. 35 and 36) is made up of trunks from the last two lumbar and first four sacral spinal nerves. There are two portions of this plexus separated by a considerable distance.

The anterior portion (Fig. 70, No. 35) consists of the lumbar nerves and a portion of the first sacral nerves. The fusion takes place on the bony ridge that separates the lumbar from the sacral region.

The posterior portion (Fig. 70, No. 36) consists of a part of the first sacral and all of the three succeeding nerves.

The anterior nerve of this plexus is distributed to the abdominal muscles. An anterior branch is given off to the sartorius. A large cutaneous branch enters between the sartorius and the ilio-trochanteric eminence, and supplies the outer and the upper surface of the upper thigh region. Several short branches are given off from the middle, or main, mass of the crural plexus to the ilio-trochanteric, or gluteal, muscle. Another nerve passes over the side of the sartorius adjacent to the femoro-tibialis, or extensor femoris, and supplies the ilio-tibialis, or gluteus primus. The rest of this 286section of the crural nerves pass in a distal direction over the inner and front side of the cutaneous nerve and enter the ilio-femoralis, or gluteus medius, the ambiens and the femoro-tibialis muscle.

The furcalis nerve comes out between the last two lumbo-sacral vertebræ.

The obturator nerve springs from several roots. The anterior root of this nerve comes from the main trunk of the crural plexus, and its last root from the furcalis nerve. The obturator nerve extends in a ventral direction from the plexus, then horizontally on the inner surface of the abdominal cavity. It gives off twigs to the obturator muscle and then passes through the obturator foramen. After leaving the abdominal cavity it gives branches to the accessorius, the obturator, and, the pubio-femoral, or adductor longus muscle.

The crural plexus gives off another large nerve trunk which extends downward. Shortly after emerging from the plexus it gives off a muscular branch to the ilio-femoralis, or gluteus medius muscle. It then passes between this muscle and the shaft of the femur, to the inner posterior surface of the thigh, and to the inner surface of the knee. It gives off a branch to the structures of the knee. At the knee this nerve terminates in several branches, some of which pass to the inner surface of the tibial head, the internal lateral ligament, the periosteum, the internal condyle, and finally to the upper part of the head of the gastrocnemius muscle.

The main part of this nerve passes downward as the cutaneous nerve, along the inner surface of the lower thigh.

The ischiadic plexus (Fig. 64, No. 41) has five to six roots, which fuse into the ischiadic trunk. This main trunk extends out of the abdominal cavity, through the ischiadic foramen, close behind the anterior trochanter of the ilium (Fig. 65, No. 1). It gives a branch to the external ilio-femoral or gluteus medius, and a branch to the post-acetabular portion of the ilio-tibialis, or gluteus primus muscle. The main trunk (Fig. 69, No. 13) passes downward to the lower portion of the thigh. In this course there are two branches which run parallel to the femoral artery and the femoral vein. It gives off a small muscular branch to the accessorius, and further down gives off a long slender branch to the outside of the knee-joint. It gives off a lateral cutaneous branch (Fig. 66, No. 7) to the posterior outer portion of the lower thigh. It supplies motor fibers to the external head of the gastrocnemius muscle.

At the knee region the ischiadica divides into three parts. The 287largest branch (Fig. 69, No. 14) passes with the tendon of the ilio-fibularis, or biceps femoris muscle, through a loop, the biceps band, and lies on the upper lateral surface of the fibula. It is covered by the external head of the gastrocnemius muscle. It innervates the three posterior muscles of the lower thigh, and then divides into two branches. One, the superficialis peroneus (Fig. 69, No. 16) passes with the profundus nerve, forming a double trunk and occupying the tibio-fibular groove on the antero-lateral side. It passes over the transverse ligament and the tibio-metatarsal joint, and after sending small branches to the structures of the tibial side of the metatarsus, it ends as a cutaneous nerve on the upper side of the third and the fourth toe.

The other branch is the peroneus profundus, which separates from the peroneus superficialis and passes downward in company with the tendons, under the transverse ligament, and then along the anterior upper surface of the metatarsus, where it innervates the muscles of that region. It gives branches to the malleolus, to the tendons of the third toe, and to the median part of the second toe, and supplies the cutaneous structures of the third and the fourth toe.

The third branch of the ischiadica, a long nerve, is given off just after the ischiadica passes through the loop. It passes downward between the two peroneal nerves. It is covered by a sheath. It passes over the posterior outside rim of the intertarsal joint and innervates the tendon sheath. The main portion of this nerve is located on the anterior surface of the tendon Achillis, and passes down on the plantar side, and innervates the periosteum and all plantar foot muscles. It finally radiates to the plantar surface of the three anterior toes.

The integument of the toes is sparingly supplied with nerves.

The nerve trunks that do not pass through the biceps band, or loop can be divided into a medial (Fig. 69, No. 15) and a lateral (Fig. 69, No. 17) portion. The medial portion (Fig. 69, No. 15) soon divides into numerous branches which supply the muscles of the posterior and the inner portion of the thigh. A rather large, long branch passes downward along the tendon of the plantar muscle, which lies on the posterior median edge of the tibia, and gives off twigs to the median and posterior part of the intertarsal joint, supplying the periosteum and other structures and the adjacent skin. It passes downward along the outer side of the medial metatarsal insertion of the tendon Achillis.

288The fifth branch is given off from the second trunk and lies laterally. It is covered by the external head of the gastrocnemius, passes along the vena saphena, and gives off a short main branch to the inner side of the intertarsal joint. The main part passes the tibial side of the joint, becomes subcutaneous, and finally innervates the two plantar muscles. A lateral ascending inner branch innervates the flexor perforatus digitorum, and, in company with an outer branch, the external head of the gastrocnemius, and also the flexor pedis perforatus.

The plexus pedundus is formed from the spinal nerves coming out of the plexus ischiadicus. These fibers emerge caudalward and are directed horizontally. They frequently anastomose with each other, especially on the pubic rim and on the outside of the plexus ischiadicus. These branches are deeply imbedded in the kidney substance and innervate the pubio-coccygeus, or depressor coccygis lateralis, the ilio-coccygeus, the transversalis, the sphincter, and other muscles of this region, and the skin of the anal region.

The Brain Coverings.—The cerebro-spinal axis of birds is similar to that of mammals. The meninges of the brain are three in number, dura mater, arachnoid, and pia mater. The dura mater is the thickest. It is constructed of white fibrous connective tissue, and lines the cranial cavity. Thus it serves as an internal periosteum. It is continuous with the spinal dura mater at the foramen magnum, and is also prolonged as a sheath of the nerves. In birds of flight where the air-sacs and reservoirs are developed to the highest state, Sappy finds that, “just as the medullary tissue is replaced by air in the bones of birds, so might it be imagined that the subarachnoid fluid is also replaced by air around the spinal cord,” and observations justify the correctness of this statement. The dura mater measures exactly the volume of the marrow in birds; so that there does not exist between the fibers and the nervous surface any space for an accumulation of liquid. This anatomical fact is sufficient to demonstrate the absence of subarachnoid fluid in the bird. In denying the existence of this fluid, it ought to be added that in this class of vertebrates, the spinal prolongation is covered by a triple envelope; and that between the pia mater and the dura mater is a thin transparent membrane, which is lubricated by a 289serous fluid. This fluid however does not collect; it only moistens the arachnoid membrane.

The arachnoid is located between the dura mater above and the pia mater below. The pia mater adheres closely to the nerve tissue.

The falx cerebri exists in fowls and in turkeys. It has the form of a segment of a circle, and extends from the middle of the interval of the openings for the olfactory nerves to the tentorium cerebelli. The falx cerebelli is absent. The tentorium is small and is sustained by a bony plate, and there are in addition two folds, one on each side, that separate the hemispheres from the tubercula quadrigemina. Owing to the absence of the falx cerebelli, the meninges lie close together. The falx cerebri is ossified in birds.

The Brain Structure.—The brain (Fig. 62, C and Fig. 75, A and C) is made up of three principal parts: the cerebrum, the cerebellum and the medulla oblongata. In a fowl of medium size the brain weighs about 150 grains.

The pons varolii is absent in birds. The crura cerebelli (Fig. 75, No. 9) are immediately connected with the corpora restiformia. The lower face of the isthmus is convex posteriorly; in front, the tubercula bigemina (Fig. 75, No. 4) are united to each other by a comparatively large transverse cord, formed by the optic nerves intercrossing in the median line. The superior face of the medulla oblongata is depressed above to constitute a fourth ventricle; in front of this ventricle are the tubercula bigemina, or optic lobes. These two voluminous tubercles are separated from each other above, where they embrace the cerebellum, and are salient on the sides of the lower face. They are hollow internally, and communicate with the aqueduct of Sylvius. The thalami optici are not well developed.

A large transverse fissure divides the cerebrum from the cerebellum (Fig. 75, No. 5). The optic chiasm (Fig. 75, No. 15) behind which lies the hypophysis (Fig. 62, No. C, 20) covers the region of the middle brain. The large transverse fissure is the dividing line between the hemispheres and the optic lobes. If the hypophysis be removed there will be observed a slit surrounded by gray matter which is called the tuber cinereum et infundibulum (Fig. 75, No. 18). On the pars commissuralis and the after brain there are visible the roots of the fifth, the ninth, the tenth, and the twelfth pairs of cranial nerves. Close beside the median furrow which extends to 290the front part of the long furrow of the spinal cord there is observed the third pair of cranial nerves, which have their origin in the middle brain. The fourth pair of cranial nerves extend from the roof of the middle brain on both sides between the middle brain and the optic lobes. These nerves finally emerge and become visible on the ventral surface.

The sixth nerve is visible near the middle furrow and almost in the middle of the pyramids, and near the roots of the fifth, the seventh, the ninth, the tenth, and the twelfth pair of cranial nerves.

The medulla oblongata (Fig. 62, No. C, 1; Fig. 75, A and C) terminates anteriorly in the pars commissuralis and the pars peduncularis. As the spinal cord approaches the head there is a gradual swelling, or lateral thickening, which merges into the medulla oblongata. The superior and the inferior surface of the medulla oblongata (Fig. 75, No. A, 1 and C, 17) are flattened. There is a shallow furrow and a slight swelling at the point where the hypoglossal nerve emerges. The central canal of the spinal cord gradually comes closer to the upper surface and communicates with the fourth ventricle, at which point the posterior raphe is shortened and the sulcus longitudinalis posterior becomes shallow. At the point where the central canal terminates in the fourth ventricle there is a V-shaped point called the calamus scriptorius (Fig. 75, No. 2). The fourth ventricle is located on the upper wall of the medulla oblongata below the cerebellum, and is bounded laterally by the peduncles of the cerebellum. It is marked posteriorly by the calamus scriptorius and anteriorly by the valve of Vieussens.

291The valve of Vieussens is located at the posterior end of the aqueduct of Sylvius. The posterior part of the fourth ventricle is marked by grooves or furrows. Extending along the central part of the floor of the fourth ventricle there is a sulcus, or groove, called the sulcus centralis, which divides the superior pyramids. On the median lateral sides there are two points of gray substance which form the alæ cinereæ. The roots of the pneumogastric, the glosso-pharyngeal, and the spinal accessory may be traced to the alæ cineræ and the gray matter of the ridges of the medulla oblongata. The sixth pair of the cranial nerves emerge from the medulla near the sulcus centralis and to the side of the auditory nerve. Part of the trigeminus emerges from the rim of the furrow next to the ridge. At the outer border of the medulla are observed the thick ends of the roots of the pneumogastric, the spinal accessory, the glosso-pharyngeal, and the auditory facialis.

On both sides of the sulcus longitudinalis inferior are found the inferior pyramids, or pyramidal columns. These pyramids become expanded near the origin of the third pair of nerves and merge into the cerebral peduncles, or crura cerebri.

The pyramidal fibers may also be traced to the optic lobes. The roots of the abducens are found at a point between the crura cerebri and the optic lobes. The third pair lies to the side of this, and the roots of the trigeminus are adjacent to those of the third. A bundle of fibers from this region pass into the cerebellum and form the crura cerebelli; others pass into the cerebellum from the side, spreading out in fan-shaped radiation, and forming the white central substances peculiarly arranged, called the arbor vitæ, or tree of life. A third bundle fuse with the crura cerebelli anteriorly, and pass into the peduncles of the cerebrum, or crura cerebri.

The gray ganglionic substance forms columns which extend the whole length of the medulla oblongata and into the cerebri. The medulla oblongata contains numerous centers which preside over various visceral functions as deglutition, respiration, thermotactic, secretory, cardiac, and digestion.

In the medulla as in the spinal cord there are five main groups of cells. First, the posterior or upper horns, from which come the somatic sensory nerves. Second, Clark’s cells, located centrally, which are the origin of the ganglionated splanchnic nerves. Third, cell groups of the lateral horns which are the center for the non-ganglionated splanchnic nerves, and certain other nerves for the 292viscera, including the enteric muscles. Fourth, cell groups of the anterior horns, which are the center of all somatic voluntary muscles. Fifth, groups of single cells probably belonging to the posterior horns which are probably centers for other splanchnic nerve fibers.

Fig. 77, A.

G, A section through the tuberculum bigeminum. 1, Pia mater. 2, Nerve fibers. 3, Fine granular ground substance. 4, Thin layer of small cells. 5, Fine granular ground substance. 6, A second thin cell layer. 7, Fine granular ground substance. 8, Third thin cell layer. 9, Fine granular ground substance. 10, Fourth widely extended cell layer. 11, A fine granular layer. 12, A thick layer of spindle cells. 13, A layer of medullated nerve fibers. 14, Ependemal cells. 15, The sinus.

H, A transverse section through the medulla oblongata, 1, 3, 4 and 6 are ganglionic centers. 2, The dorsal groove. 8, The ventral fissure. 5, The central canal. 7, Fiber tracts.

I, A transverse section through the cervical portion of the spinal cord. 1, Ventral septum. 2, Dorsal septum. 3, The central canal. 4, The dorsal horn. 5, The ventral horn.

J, A section through the wall of the oil gland, or rump gland. 1, The stroma. 2, The tubular glands some of which are branched.

K, A section through a spike of a comb of a cock. 1, The epithelial layer. 2, A dense fibrous subepithelial layer. 3, A second fibrous vascular layer. 6, A denser central core supporting the large arteries and veins. 4, A vein. 5, An artery.

L, A section through a lobe of the wattle of a hen. 1, The epithelial layer. 2, A dense vascular layer. 3, A vein. 4, An artery. 5, A loose fibrous vascular structure.

The gray matter in the cord is in the form of two commas placed with their backs together with the central canal passing between 293them. The central canal is located in the center of the cord. As the cord nears the medulla oblongata the form of the gray matter changes. The second, the third, and the fifth ganglion centers are arranged laterally, and show a distinct side-horn group. The central canal separates the two Clark’s columns; later the side-horn group enlarges and extends ventrally around the anterior horn group and joins on the other side in half-moon shaped formation.

The central ganglionic mass of the spinal cord, the center for the enteric visceral system, is divided into three complex parts. First, there are cell groups on both sides of the posterior raphe. Second, the half-moon shaped ventral groups extending parallel peripherally described above. Third, lying between groups one and two a complex group, which possesses a large collection of cells. These furnish splanchnic nerve centers, the anterior supplying motor nerves and carrying motor impulses outward, and the superior sensory which carry impulses to the centers. The cell group of the superior horns takes a sidewise peripheral position (Gadow).

The cerebellum (Fig. 62, C, 2) is located above the medulla oblongata and posterior to the cerebrum. The cerebellum consists principally of a median lobe called the worm. The lateral lobes are conical and rudimentary. The under part of the worm forms the roof of the fourth ventricle.

On the upper surface of the cerebellum are numerous transverse markings (in the hen 13 or 14) which divide the lobe into leaves. When the cerebellum is cut lengthwise there is observed on the sectioned surface the peculiar arrangement of the white and the gray matter, the arbor vitæ, mentioned above. There is a small cavity in the cerebellum which communicates with the fourth ventricle.

The cerebellar cortex shows four parts, namely: First, the central part composed of white medullated fibers, between which are arranged neuroglear cells. Second, a rather reddish layer of cells of different sizes. These cells are embedded in a fine ground substance and are about 0.003 mm. in diameter. Third, a plain layer of large pear-shaped ganglion cells, the cells of Purkinje. Fine branches extend outward from the apex of these cells. Fourth, an outer gray layer which consists of small multipolar nerve cells with some neuroglear cells. The color of these three layers, according to Gadow, depends upon the color of the plumage; that is, if the plumage is dark, this layer is dark; if light, the layers are 294light. The marked coloring is said to be most distinct in the second layer.

The anterior portion of the cerebellum consists of medullated nerves whose fibers run crosswise. These are the extensions of the true cerebellar fibers, which become fewer and fewer as they proceed anteriorly. Finally, a few remaining fibers running crosswise fuse as the commissura Sylvii, and extend into the lobi optici. A layer of nerve cells extends under these medullated nerve fibers.

A bundle of fibers extending from the medulla oblongata. These fibers extend into the optic lobes, form the crura cerebri, or peduncles of the cerebri, and also form the inferior wall, or floor, of the aqueduct of Sylvius. The crura are sometimes spoken of as the partes pedunculares. These contain gray matter. The following division is made of the ganglion of this region. First, a group of cells near the base of the peduncles, which are divided from the ventral rim by the arciform fibers. This ganglionic formation may be considered an extension from the medulla oblongata. Second, a group of the ganglion cells of the lobus optici. Third, a group of cells lying near the lobus opticus, which give rise to the ascending roots of the trigeminus. Fourth, a group of ganglionic cells from which spring the roots of the motores occuli, and which lies near the middle line and under the sulcus centralis. Many ganglion cells are found to the right and to the left of the sulcus centralis, which show different arrangement of the cells at different levels. Fifth, a group of irregular cells which extends centrally on the superior walls of the third ventricle and to the superior part of the lobus opticus.

The microscopic structure of the roof of the lobus opticus, or corpus bigeminum, shows that the layers are arranged parallel to the pia mater and are divided into the following parts:

Externally, the pia mater.

An outer layer of very fine nerve fibers, which lies just below the pia mater.

A layer of fine granular ground substance.

A thin layer of small cells the diameter of each of which is 0.038 mm.

A layer of fine granular ground substance.

A second thin cell layer.

A zone of fine granular ground substance.

A third thin cell layer.

295A fine granular ground substance.

A fourth widely extended cell layer.

A fine granular layer.

A somewhat thick layer of spindle-shaped cells.

A layer of medullated nerve fibers.

This last is the inner layer of nerve fiber. On the inner surface of this layer we find the ependymal cells, the cells that line the cavity of the optic lobes. The commissura Sylvii form the covering of the lobi optici and join these two lobes. This commissure is formed from the upper and the lower layer of nerve fibers. In the commissure these fibers cross each other.

The hypophysis (Fig. 62, No. C, 20) lies back of the chiasm, or optic commissure, and below the middle of the third ventricle. The infundibulum, a pedicle-like structure, connects the hypophysis with the third ventricle of the cerebri. It contains a cavity and forms an extension of the third ventricle. The hypophysis is divided into two lobes, an anterior and a posterior.

The third ventricle communicates anteriorly with the lateral ventricles of the cerebri through the foramen of Monro, and posteriorly with the fourth ventricle through the aqueduct of Sylvius. The posterior walls of the third ventricle are relatively thick and form the posterior brain commissure. The wall is thin from the commissure to the chiasm. Within it lie two ridges, which connect the two hemispheres with the corpus callosum, and, farther anteriorly, with the anterior cerebral commissure. The space from the third ventricle and to the anterior commissure is called the laminæ terminales.

The pineal gland, located between the cerebri and the cerebellum, lies against the choroid plexus, which covers the highest point of the third ventricle.

The cerebrum is divided by a deep longitudinal fissure into two hemispheres. The cerebrum is shaped somewhat like the heart on a playing card. The lower face is somewhat flattened. The upper and lateral sides are not provided with convolutions or sulci, but are smooth. The fissure of Sylvius is faintly marked on the inferior face. The olfactory lobes appear well developed and are relatively large for the size of the brain. They lie close together on the extreme anterior portion in the median line.

The olfactory cerebral crura emerge from the cranium at the upper angle between the posterior wall, the roof, and the septum of 296the orbit, and pass through the olfactory foramina and in grooves on the upper part of the septum; then passing forward they penetrate the frontal structure and are finally distributed over the turbinated mucous membrane.

The corpus striatum is large; it occupies nearly the entire floor of the ventricles.

The anterior commissure is found between the hemispheres. Its middle part lies in the lamina terminalis on the division between the anterior and the middle brain, and close to the thalami optici. Its side extensions are rounded masses called the nervi amygdales.

The corpus callosum, quite rudimentary, lies on the posterior dorsal rim of the anterior commissure.

The corpus striatum forms a thin broad ridge, which passes ventrally. This structure consists of twenty-five large pyramidal cells which lie in the posterior lateral dorsal section, and of from ten to fifteen pyramidal cells which are located in the rest of the section. In addition to these two groups there are many cells about 5 millimeters in diameter. These lie, six or more, in a nest imbedded in neuroglia. There is a thin layer of spindle cells near the ventral line. The outer nerve nest, or nerves amygdalis, lies in the posterior lateral ventral part. It is covered by a thin membranous layer. Its cells are pyramidal in shape and are from 10 to 15 millimeters in diameter. The cells terminate in spindle form toward the periphery. Nerve fibers extend from the anterior commissure.

The outer wall of the corpus striatum consists of the following layers:

An outer white layer consisting of fine medullated nerve fibers imbedded in a ground substance containing numerous nerve cells.

A layer of ganglionic cells, consisting of pyramidal cells from 10 to 15 millimeters in diameter, of other round cells 20 millimeters in diameter, and finally of cells only 5 millimeters in diameter. This layer forms a reddish line in the dorsal portion of the corpus striatum.

These layers form part of the median and the posterior cerebral wall of the lateral ventricle. The lateral ventricle is closed except for a slit-like opening behind the posterior commissure. This is the foramen of Monro, through which the lateral ventricle communicates with the middle, or third, ventricle.

The choroid plexus is found at the base of the lateral ventricle.

The wall of the lateral ventricle becomes thinner near the region of the transverse commissure on the surface toward the middle 297brain. At this point the pia mater and the ependyma, or the lining cells of the ventricular membrane, form the major part of the wall.

The domestic fowl does not have the hippocampus.

The wall of the middle ventricle consists of an outer white layer, which is arranged similarly to that of the corpus striatum. The ventral rim of the wall is formed by a spiral band which consists of fine medullated fibers, in which are imbedded a few cells.

The processus cerebri mammillares are also called the tubercula olfactoria. From these structures extend forward the olfactory nerves, the posterior roots of which may be traced to the walls of the lateral ventricles.

The structure of the processus cerebri mammillaris is made up of five layers as follows:

An outer layer, which consists of colorless olfactory fibers extending in all directions.

A granular ground substance layer, in which are imbedded a few cells.

A thicker granular layer, on the inner edge of which are twenty large pyramidal cells with processes pointing outward.

A layer of closely packed cells, in which are fine medullated nerve fibers. These cells are about 5 millimeters in diameter.

An innermost layer of ependymal cells.

Near the hemisphere the peripheral nerve fibers and nerve cells disappear, leaving only the ground substance of the processus to aid in the formation of the hemisphere.

There is a long bundle of fibers on the lower surface of the hemisphere, which blends with the substance of the olfactory fibers.

The peduncles of the cerebrum (Fig. 62, No. 21) are the slightly diverging columns of nerve tissue, which form the anterior continuation of the medulla oblongata and disappear under the optic tracts and the chiasm.

The sympathetic nervous system commences anteriorly at the large superior cervical nerve ganglion. This ganglion, anteriorly, brings into communication the glosso-pharyngeal, the pneumogastric, or vagus, and the sympathetic system.

The following nerve trunks emerge from the superior cervical nerve ganglion: a large trunk fusing with the vagus and directed 298downward, accompanying and surrounding the carotid artery; a second large trunk fusing with the recurrent pharyngeus and the glosso-pharyngeus; a third trunk which merges with the hypoglossal; finally several trunks which are distributed to the head.

The temporo-lacrimalis, one of the large sympathetic nerves of the head, as it extends from the cervical nerve ganglion, receives branches from the ganglion radicis vagi. This nerve, passing between these two ganglions, extends horizontally forward and outward through a foramen, crossing the glosso-pharyngeus. Near the Fallopian canals it crosses the facial nerves, lies supero-laterally, and receives a short branch from the facial nerve whose fibers are traceable to the geniculate ganglion. It also receives a branch from the recurrent maxillaris.