Chapter VI: Part II: 1, The os occipitale (1, dorsal; 2, two lateral; 3, ventral (5)

The remains of the umbilical veins are traceable within the duplicature of the membranes forming the septum. These remains thus represent the round ligament of mammals.

FIG. 38.—Cellular structure of liver, pancreas, and trachea.

_A._ Liver. 1, Liver cells. 2, Sinusoid. 4, Nucleus of cells.

_B._ Pancreas. 1, Island of Langerhans. 2, Alveolar cells. 3, Duct.

_C._ Trachea. 1, Ciliated epithelia. 2, Glands. 3, Hyaline cartilage.

_D._ Section of wall of ovum at Fig. 57 letter _d_. 1, Yolk. 2,
Granular membrane. 3, Theca. 4, Blood-vessel.
]

A microscopic study of the liver of the fowl shows a compact mass of liver cells polyhedral in shape, with large nuclei (Fig. 38, _A_). The liver tissue differs from that of mammals in that there is no clearly outlined lobular arrangement; neither is the outline of the individual cell so well marked. The parenchymatous portion is made up of columns of liver tissue. These columns anastomose and show narrow channels between. They are best seen in the young chick.

_Function._—One of the functions of the liver is to secrete bile. A _gall-bladder_, which receives part of the bile secreted by the right lobe of the liver, is located on the posterior face of this lobe. Extending from this gall-bladder there is a duct, the _cystic duct_, which empties into the small intestine toward the extremity of the second branch of the duodenal loop. Another duct called the _hepatic duct_, proceeds directly from the two lobes of the liver and empties into the intestine just in front of the cystic duct.

=The Pancreas= (Fig. 31, No. 17). _Location and Shape._—The pancreas, an organ lying in the duodenal loop is a yellowish-white, lobulated gland, elongated in shape. Its average length in fowls of average size is 4.96 inches, and the average weight about 0.008 pound. The pancreas is divided into lobes, which in turn are divided into lobules.

_Structure._—The pancreas has a supporting connective tissue. The lobules are made up of small alveolar glands, which are lined with columnar epithelial cells. The ducts leading from the alveoli are small; these unite to form larger ducts in which the epithelium is taller. Between the alveoli throughout the pancreas there are clusters of polyhedral cells which form the _islands of Langerhans_. These islands are said to produce an internal secretion, or hormone, which is absorbed by the blood or lymph capillaries and thus enters the circulation (Fig. 38, _B_).

_Function._—The function of the pancreas is to secrete a fluid containing digestive ferments.

=The Spleen= (Fig. 31, No. 21). _Location._—The spleen, or lien, lies in a triangle formed by the proventriculus, the liver, and the gizzard.

_Shape._—It is a reddish-brown body shaped like a buckeye, is small in size, weighing only about 0.005 pound.

_Structure._—The outer surface of the spleen is covered by a reflection of the peritoneum. After this covering is removed, there is observed a firm, white, fibrous layer, the _cortical portion_. This covering sends into the interior small and large trabeculæ, forming a framework and dividing it into acini, or compartments. The spaces are filled with a dark red parenchymatous material called _splenic pulp_. The framework, in both deep and surface portions, are found elastic fibers and smooth muscular fibers.

The spleen is essentially a lymphatic organ, its peculiar structure depending largely upon the arrangement of the blood-vessels. Compact lymphatic tissue occurs in the spleen in spherical, oval, or cylindrical collections of closely packed lymphoid cells. These masses are known as the _Malpighian bodies_, or _splenic corpuscles_. They are distributed throughout the splenic pulp. Each splenic corpuscle contains one or more small arteries. These extend near the periphery of the corpuscle and more rarely in the center.

The splenic artery passes in and the splenic veins out at the hilum which is located on the concave, or attached, side of the spleen. The splenic artery, upon entering the organ, at once branches, the trabeculæ forming a support for the vessels.

After the arteries have entered the hilum, as stated above, they divide into many branches which follow the septa of the connective tissue. At first the arteries are accompanied by branches of the splenic veins. Soon, however, the arteries leave the veins and the septa, and penetrate the splenic pulp. In the splenic pulp the adventitia of the smaller arteries assume the character of reticular tissue, and become infiltrated with lymphoid cells. This infiltration forms masses which are called the splenic corpuscles, or Malpighian bodies. The terminal arteries break up into capillaries, which still retain an adventitia, and empty into border spaces, or sinuses, sometimes spoken of as ampullæ. These sinuses in turn empty into cavernous sinuses of the splenic pulp. From these are finally formed the venules; and the collections of venules form the splenic veins through which the blood gains exit from the spleen.

=The Abdominal and Pelvic Cavities.=—In birds the abdominal cavity is divided into two smaller cavities by a fibrous septum. The anterior cavity representing the abdominal contains the liver, and the other representing the pelvic contains the gizzard, intestines and oviduct.

=The Peritoneum and the Mesentery.=—The abdominal and pelvic cavities are lined by the peritoneum. Like all serous membranes this is composed of a parietal and a visceral portion, which together form a complete sac, with the organs it covers situated on the outer side. The peritoneum like other serous membranes consists of a mesothelial and a submesothelial portion, the cells of the former being arranged in a single layer. Since a serous membrane is so arranged as to line a closed cavity, and at the same time to cover its contents, it follows that the entire membrane must be a closed sac, the mesothelial layer being on the inside; such a sac is called a serous sac, or cavity. Synovial membranes are also regarded as a variety of serous membranes. The fold, or layer, of the membrane which lines the cavity is called the parietal, that which covers the greater part of the organs contained therein is called the visceral portion; the two surfaces contacting, and gliding upon each other, are lubricated by a fluid secretion contained in the sac; hence one use of these membranes is to prevent friction between the walls of cavities and the organs contained therein. Serous membranes line the abdominal cavity, pericardium, cavities of the heart and is continuous throughout the vascular structures.

FIG. 39.—A transverse section of body of hen through 15, Fig. 34. _R_,
Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus. 3,
Trachea. 4, Skin. 5, Pectoral muscles.
]

The serous membrane besides covering the external surface of the viscera, double folds pass from one organ to another, or from an organ to the parietes of the cavity. These double folds of the peritoneum are known as ligaments, or as mesenteries. In ligaments the two folds are strengthened by an interposed layer of fibro-elastic tissue. A _mesentery_ is a broad, double fold of peritoneum, attached to the abdominal parietes above, and containing a portion of the intestine in its free or remote extremity. Between its folds we find blood-vessels, nerves, and lymphatics or lacteals, hence it permits vascular and nervous communications with the organ attached to it. The free portion of the small intestine is attached to the free margin of the mesentery.

THE RELATIONS OF THE VISCERAL ORGANS OF THE DOMESTIC FOWL

FIG. 40.—Transverse section through the body of a hen through 14, Fig.
34. _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus.
3, Trachea near inferior larynx. 4, Lungs. 5, Pectoral muscles.
]

Figure 33 shows a fowl with the left abdominal wall and the left thoracic wall removed. No. 1 in this figure shows the base of the heart in front of the left lobe of the liver. Above the liver is the proventriculus; above this, the diaphragm; and above the diaphragm and the base of the heart the left lung occupying the superior part of the thoracic cavity, and that there is no distinct pleural sac, as in mammals but that the lung pushes out between the ribs, thus pressing against the ribs on the inner and the lateral sides. The gizzard is back of the liver, to the left side of the abdominal cavity, and beneath and in front of the duodenal loop. The small intestine from this side is above the gizzard. Supero-anterior to the gizzard is the blind end of the cæcum. The pancreas is within the duodenal loop.

FIG. 41.—Transverse section through the body of a hen at 12, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus. 3,
Inferior larynx. 4, Base of the heart. 5, Aorta. 6, Vena cava. 7,
Lungs. 8, Skin. 9, Pectoral muscles.
]

Figure 34 shows the viscera from the right side after the removal of the right abdominal and the right thoracic wall. The base of the heart is in front of the right lobe of the liver. Above these the right lung occupies the upper part of the thoracic cavity as in the preceding illustration. Just back of this is the anterior lobe of the kidney. The gall-bladder is observed at No. 9 on the right lobe of the liver. Just inferior to a longitudinal central line is the duodenal loop, between the limbs of which is seen the pancreas. Above this loop the cæca are located. The gizzard is not visible from the right side; on this side posterior to the liver is the small intestine. Superior to this at No. 7 the rectum.

The relative position of the visceral organs in the median line is observed in Fig. 35. No. 1 of this figure shows the stump of the first portion of the esophagus, and No. 2, the left wall of the crop. Following this, and located just below the vertebræ is the second portion of the esophagus. The major portion of the crop is located on the right side.

FIG. 42.—Transverse section through the body of a hen at 11, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Vertebra. 3,
Spinous process of vertebra. 4, Lungs. 5, Esophagus. 6, Pericardial
sac. 7, Sectioned surface of heart. 8, Auricle of heart. 9, Blood
clot in right auricle. 10, Section of sternum. 11, Pectoral muscles.
]

It will be noted that the second portion of the esophagus passes over the base of the heart and the superior part of the liver, and then terminates in the proventriculus. The proventriculus extends downward and empties into the gizzard. This organ lies antero-laterally to the gizzard, supero-posterior to the liver, and to the left of the spleen. The spleen lies in a triangle formed by the liver, the proventriculus, and the gizzard. The heart is noted to lie supero-anterior to the liver, and between the anterior portion of the fissure formed by the right and the left lobe. The ovary is located back of the diaphragm at the anterior end of the kidney and below the inferior surface of the bodies of the vertebræ. The bulk of the floating portion of the small intestine is located above the gizzard.

FIG. 43.—Transverse section through the body of a hen at 13, Fig. 34.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Body of
vertebra. 3, Superior spinous process of vertebra. 4, Lungs. 5,
Esophagus. 6, Heart. 7, Right and left lobes of liver. 8, Sternum.
9, Skin. 10, Pectoral muscles.
]

A transverse anterior section of a normal laying hen is shown in Fig. 39, the section being made at 15 of Fig. 34. At this point the esophagus lies centrally and above the trachea. Figure 40 shows a transverse anterior section through the thoracic region at 14 of Fig. 34. At this point the esophagus is slightly to the right of and is superior to the trachea. At this level the apex of the lung is sectioned. This is in the region of the cervical air-sac. Figure 41 shows a posterior section at 12 of Fig. 33. The esophagus here is above and to the right of the inferior larynx, and directly below and between the lungs. The inferior larynx is above the base of the heart.

Figure 42 shows a transverse anterior section made at 11 of Fig. 33. It shows that at this level the esophagus is centrally located and passes over the base of the heart. The heart occupies the lower portion of the thorax and the lungs the upper. Figure 43 shows a photograph of a transverse anterior section of the body made at 13 of Fig. 34. At this level the apex of the heart lies within the anterior fissure of the liver. The sectioned portion of the heart shows the lower portion of the ventricle.

FIG. 44.—Transverse section through the body of a hen at 12, Fig. 34.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Articular
surface of vertebral segment. 3, End of rib. 4, Lungs. 5,
Proventriculus. 6, Liver showing Glisson’s capsule. 7, Sternum. 8,
Pectoral muscles. 9, Skin.
]

FIG. 45.—Transverse section through the body of a hen at 10, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Body of
vertebra. 3, Lungs. 4, Ova. 5, Proventriculus. 6, Liver. 7, Sternum.
8, Skin. 9, Pectoral muscles.
]

In this figure the lungs show, on the sectioned surface, the ends of some of the larger bronchi. The esophagus is located above the heart. Showing the relations of the visceral organs back of the heart girdle, photograph number 44, gives an anterior section made at 12, Fig. 33. The lungs are spread out occupying the posterior thoracic region and below at No. 10 is the diaphragm. The diaphragm does not appear to have that rigidity and firmness of position as in mammals. It is rather rudimentary. Below the left lung and above the left lobe of the liver is the proventriculus. Note that the viscus is empty and that the mucous membrane is thrown into folds. At this point the liver occupies much of the abdominal cavity. Figure 45 is a view of an anterior section made at 10, Fig. 33. In this section the lungs are decreasing in caliber. The liver occupies much of the space in the lower right abdominal quadrant, and above and to the right is the ovary with many of the ova developing yolks. Below No. 4 which is a developing yolk, is the proventriculus. Figure 46 is a view of an anterior section made at 9, Fig. 33. At this level are shown sectioned surfaces of the kidneys, which lie on either side of the spinal column. Below the spinal column and occupying the left upper quadrant is the ovary containing ova in the process of developing yolks. To the right is the sectioned surface of one of the cæca and below this and on the right side is the sectioned ends of many of the loops of the floating portion of the small intestine. Occupying the left lower quadrant is the sectioned surface of the gizzard and on the abdominal floor and to the right of the gizzard, the posterior end of the right lobe of the liver.

FIG. 46.—A transverse section through the body of a hen at 9, Fig. 33.
_R_, Right side. _L_, Left side. 1, Spinal cord. 2, Vertebra. 3,
Kidneys. 4, Ovary. 5, Cæcum. 6, Small intestine. 7, Gizzard. 8,
Right lobe of liver. 9, Skin. 10, Pectoral muscles.
]

THE RELATIONS OF THE VISCERAL ORGANS OF THE BABY CHICK

There is approximately 47 per cent. of the yolk retained in the abdominal yolk sac of the baby chick at hatching. Figure 47 shows a photograph of a longitudinal section through a baby chick. This figure shows all the posterior portion of the abdominal cavity occupied with abdominal yolk. The abdominal viscera are pushed forward, and as the yolk is gradually absorbed the visceral organs gradually occupy their normal position.

FIG. 47.—An antero-posterior section through the body of a baby chick
just hatched. 1, Abdominal yolk sac. 2, Gizzard. 3, Liver. 4, Heart.
5, Intestines. 6, Spinal cord. 7, Cerebrum. 8, Cerebellum. 9, Fat in
the post-occipital region. 10, The thymus gland.
]

FIG. 48.—Transverse sections of the body of a baby chick at hatching.
_R_, Right side. _L_, Left side.

_A._ A transverse section at _A_, Fig. 50. 1, Spinal cord. 2,
Esophagus. 3, Entrance to thorax. 4, Stubs of the wings.

_B._ A transverse section at _B_, Fig. 50. 1, Spinal cord. 2,
Esophagus. 3, Lungs. 4, Heart.

_C._ A transverse section through the body at _C_, Fig. 50. 1, Spinal
cord. 2, Lungs. 3, Esophagus. 4, Liver. 5, Heart.

_D._ A transverse section at _D_, Fig. 50. 1, Spinal cord. 2,
Proventriculus. 3, Liver. 4, Gizzard. 5, Intestine. 6, Kidneys. 7,
Gall-bladder.
]

FIG. 49.—Transverse section through the body of a baby chick.

_E_ at _E_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3, Gizzard. 4,
Intestines. 5, Unabsorbed yolk. 6, Stubs of legs.

_F._ A section at _F_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3,
Intestine. 4, Unabsorbed yolk.

_G._ A section at _G_, Fig. 50. 1, Anus. 2, Umbilicus.
]

A section through this body Fig. 47 at _A_ is shown in Fig. 48, _A_. At this point the esophagus appears below the vertebral column. Figure 48, _B_, a section through the body at Fig. 47, _B_, shows the apex of the lungs. In a median line and below the lungs is the esophagus. Note the mucous membrane thrown into folds. Here the heart is sectioned, showing both auricles and both ventricles. This is a view looking forward. Figure 48, _C_, is a view of a posterior section made at Fig. 47, _C_. It shows the same relations of the esophagus and lungs, but shows at this level both the right and the left lobe of the liver. Between these lobes we note the sectioned apex of the heart. Figure 48, _D_ shows a posterior section at Fig. 47, _D_. At this level the kidneys are above and infero-laterally to the spinal column. The intestines are below the kidneys; and on the left side, between the kidneys and left lobe of the liver, and near the abdominal wall, is the proventriculus. Occupying the major portion of the inferior abdominal cavity are the right and the left lobe of the liver, and between these the anterior border of the gizzard. Note the gizzard sitting at an angle inclining toward the left side. Figure 49, _E_ shows a section at Fig. 47, _E_. Here the gizzard occupies the left lower abdominal quadrant. To the right are the intestines; and directly above the gizzard is a small portion of the anterior end of the abdominal yolk sac. Infero-laterally are the kidneys. Figure 49, _F_, shows the kidneys similarly located as in the preceding; and just below is the rectum suspended by the mesentery. The rest of the cavity is occupied by the abdominal yolk.

THE URO-GENITAL SYSTEM

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 (Fig. 50 and Fig. 51).

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 itself. 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 lobules. 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. 1_a_, The posterior. 1_b_, the middle and 1_c_,
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.
]

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.
]

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 cuboidal 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 the 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 (Fig. 54)

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.

_Structure._—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.

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.
]

In 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 (Fig. 56)

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 active 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. 2). 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.

The _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 per 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]

Footnote 6:

The analysis was made by D. M. McCarty, chemist, Animal Industry
Division, North Carolina Experiment Station.

Moisture 64.25 per cent.
Dry matter 35.75 per cent.
————————————————
100.00 per cent.

Parts per hundred including
shell

Protein 10.2500
Fat 10.6200
Phosphorus .3020
Calcium .6080
Magnesium .0985
Iron .0103
Sulphur .3950
Chlorine .1506
Potassium .0103
Sodium .2000

=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 the 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).

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 layers 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_).

It 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.

The 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 ciliated 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 anteriorly 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.