Part 58

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. 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. ]

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.