Part 51

=Fixation.=—Displacement of the bladder is limited chiefly by three peritoneal folds, termed the middle and lateral ligaments (Figs. 257, 272). The =middle ligament= (Plica umbilicalis media) is a median triangular fold, formed by the reflection of the peritoneum from the ventral surface of the bladder on to the ventral wall of the pelvis and abdomen. In the new-born animal it is extensive and reaches to the umbilicus; in the adult it is usually much reduced in length relatively. It contains elastic and muscular fibers in its posterior part. The =lateral ligaments= (Plicæ umbilicales laterales) stretch from the lateral aspects of the bladder to the lateral pelvic walls. Each contains in its free edge a round, firm band, the =round= or =umbilical ligament= (Lig. umbilicale s. teres); this is the remnant of the large fœtal umbilical artery, the lumen of which in the adult is very small. The retroperitoneal part of the bladder is attached to the surrounding parts by loose connective tissue, in which there is a quantity of fat. It is evident that the posterior part of the bladder has a definite fixed position, while its anterior part is movable.

=Structure.=—The wall of the bladder consists of a partial peritoneal investment, the muscular coat, and the mucous lining.

The =serous coat= (Tunica serosa) covers the greater part of the dorsal surface, from which it is reflected in the male to form the urogenital fold; in the female it passes on to the vagina, forming the vesico-genital pouch. Ventrally the peritoneum covers only the anterior half or less of the bladder, and is reflected posteriorly on to the pelvic floor.

The =muscular coat= (Tunica muscularis) is relatively thin when the bladder is full. It is unstriped, pale, and not clearly divided into layers, but has rather a plexiform arrangement. Longitudinal fibers occur on the dorsal and ventral surfaces, but laterally they become oblique and decussate with each other. A distinctly circular arrangement is found at the neck, where the fibers form a =sphincter= (Annulus urethralis).

The =mucous coat= (Tunica mucosa) is pale and thin. It is in general attached by a highly elastic submucosa to the muscular coat, and forms numerous folds when the organ is empty and contracted. It is modified dorsally in the vicinity of the neck over a triangular area, termed the =trigonum vesicæ=; the angles of this space lie at the orifices of the two ureters and the urethra, which are close together. Here the mucous membrane is closely attached and does not form folds. From each =ureteral orifice= (Orificium ureteris) a fold of mucous membrane (Plica ureterica) passes backward and inward, uniting with its fellow to form a median crest (Crista urethralis) in the first part of the urethra. The ureteral orifices are a little more than one inch (ca. 3 cm.) apart. The terminal part of the ureter, after piercing the muscular coat of the bladder, passes for a distance of about an inch (ca. 2 to 3 cm.) between the muscular and mucous coats before piercing the latter; this arrangement constitutes a valve which prevents absolutely the return of the urine from the bladder into the ureter. The =internal urethral orifice= (Orificium urethæ internum) lies at the apex of the trigonum, and is about an inch and a half (ca. 4 cm.) behind the ureteral orifices. The mucous membrane is covered with transitional epithelium like that of the ureter and renal pelvis. It contains lymph nodules.

=Blood-supply.=—This is derived chiefly from the vesico-prostatic branch of the =internal pudic artery=. It is also supplied by small twigs from the =obturator= and =umbilical arteries=. The =veins= terminate chiefly in the =internal pudic veins=. They form plexuses posteriorly.

=Lymph Vessels.=—These form plexuses on both surfaces of the muscular coat. They go to the internal iliac and lumbar glands.

=Nerves.=—The nerves are derived from the =pelvic plexus= (sympathetic and ventral branches of third and fourth sacral nerves). They form a plexus in the submucosa which presents microscopic ganglia.

In the fœtus and new-born animal the bladder is situated chiefly in the abdomen. It is long, narrow, and fusiform. Its abdominal end lies at the umbilicus, through which it is continued by the urachus to the extra-embryonic part of the allantois. As the pelvis increases in size and the large intestine grows, the bladder retracts into the pelvis and changes its form.

The urethra will be described with the genital organs.

THE ADRENAL BODIES

The =adrenal bodies= or =suprarenal glands= (Glandulæ suprarenales)[142] are two small, flattened organs, which lie in contact with the anterior part of the inner border of the kidneys (Figs. 376, 377). They are ductless.

In the horse they are red-brown in color, about three and a half to four inches (ca. 9 to 10 cm.) long, one to one and a half inches (ca. 3 to 4 cm.) wide, and about half an inch or more (ca. 1 to 5 cm.) in thickness. The weight varies from one to two ounces (ca. 28 to 56 gm.).

The =right adrenal= is related internally to the posterior vena cava, to which it is adherent. Its anterior part curves dorsally around the inner border of the right kidney. Its posterior part is flattened and is related ventrally to the pancreas and cæcum, dorsally, to the right renal vessels. The anterior extremity is concealed in the renal impression of the liver; the posterior is related to the ureter.

The =left adrenal= is a little shorter than the right one, and its extremities are rounded; it is usually curved, so that its internal border partly embraces the anterior mesenteric artery. Its dorsal surface is related to the kidney, the renal artery, the aorta, and the left cœliaco-mesenteric ganglion. The ventral surface is in relation with the left extremity of the pancreas and the root of the great mesentery. The posterior extremity often curves inward behind the anterior mesenteric artery; it is related behind to the left renal vein.

When hardened _in situ_ the adrenals present several features not evident in the soft organs. The anterior part of the right adrenal is twisted upward and outward over the inner margin of the kidney, so that this part is prismatic and has three surfaces; of these, the concave outer one is applied to the kidney, the dorsal one is related to the right crus of the diaphragm and the liver, and the inner one is in contact with the posterior vena cava. The anterior mesenteric artery is nearly always more or less enlarged as a result of verminous arteritis, and the form and degree of curvature of the left adrenal seem to vary in conformity with the condition of the artery.

=Structure.=—The =fibrous capsule= adheres intimately to the surface of the organ. It contains elastic fibers, and in its deep part unstriped muscle-fibers. From it trabeculæ pass radially into the substance, blending with the fine supporting reticulum. The =parenchyma= consists of a cortical and a medullary portion. The =cortical substance= (Substantia corticalis) is red-brown in color, and is clearly distinguishable from the yellow =medullary substance= (Substantia medullaris). A large =central vein= (Vena centralis) is visible on cross-sections.

The cells of the cortex are arranged in chains of one or two rows. In the peripheral portion the cells are of high cylindrical shape, and the chains form connecting loops; Günther has proposed the name zona arcuata for this part, instead of the usual term zona glomerularis. More deeply the chains are distinctly palisade-like, and this region is called the zona fasciculata. Next to the medulla is the zona reticularis, in which the chains form a network. The cells in these two zones are polygonal and contain a brown pigment.

The cells of the medulla are arranged in irregular groups or form sheaths around the veins. They react to chromic salts by assuming a yellow or yellow-brown color, and are termed chromaffin cells; they share this peculiarity with certain cells of the sympathetic ganglia and paraganglia, with which they are probably related genetically. The alkaloid adrenalin appears to be formed in the medullary cells.

=Vessels and Nerves.=—The adrenals receive a relatively large blood-supply through the =adrenal arteries= (Aa. suprarenales), which arise from the renal arteries or from the aorta directly. The =veins= terminate in the posterior vena cava and the left renal vein. The =lymph vessels= go to the renal lymph glands. The numerous =nerves= are derived from the sympathetic system through the solar and renal plexuses. The fibers form a rich interlacement, especially in the medullary substance. Ganglion cells are found chiefly in the medulla, but also occur in the deeper part of the cortex.

[Illustration:

FIG. 381.—ADRENAL BODY OF HORSE; HORIZONTAL SECTION, REDUCED.

_1_, Capsule; _2_, _2′_, cortical substance; _3_, medullary substance; _4_, blood-vessel in section. (From Leisering’s Atlas, reduced.) ]

URINARY ORGANS OF THE OX

The =kidneys= are superficially divided into polygonal lobes by fissures of variable depth. The lobes vary in size, and are commonly about twenty to twenty-five in number. The fissures are filled with fat.

The =right kidney= has an elongated elliptical outline, and is flattened dorso-ventrally. It lies ventral to the last rib and the first two or three lumbar transverse processes. The dorsal surface is rounded, and is in contact chiefly with the sublumbar muscles. The ventral surface is less convex, and is related to the liver, pancreas, duodenum, and terminal part of the colon. The hilus is situated on the anterior part of this surface near the inner border. The internal border is nearly straight, and lies parallel with the posterior vena cava. The external border is convex. The anterior extremity occupies the renal impression of the liver, and is capped by the adrenal body.

The =left kidney= occupies a remarkable position, and when hardened _in situ_, differs strongly in form from the right one. When the rumen is full, it pushes the kidney backward and across the median plane, so that it is situated on the right side, behind and at a lower level than the right kidney. It then lies usually under the third, fourth, and fifth lumbar vertebræ. When the rumen is not full, the left kidney may lie partly to the left of the median plane. It has three surfaces. The dorsal surface is convex, and presents on its antero-external part the hilus, which opens outward. The ventral surface is related to the intestine. The third face is often more or less flattened by contact with the rumen, and may be termed the ruminal surface. The anterior extremity is small, the posterior large and rounded.

[Illustration:

FIG. 382.—RIGHT KIDNEY OF OX, VENTRAL FACE.

Organ hardened _in situ_. Fat has been removed from fissures between lobes. ]

The preceding statements refer to the adult subject, and are based on investigations made on living subjects, and studies of frozen sections and material hardened _in situ_. In the young calf the kidneys are almost symmetrically placed, but as the rumen grows it pushes the left kidney to the right and backward _pari passu_. It also usually causes a rotation of the kidney, so that the primary dorsal surface comes to lie almost in a sagittal plane. Further, the gland is bent so that the hilus is largely closed up and faces outward (to the right). In very fat subjects the three-sided appearance of the kidney may be absent, and about one-third or more may remain to the left of the median plane, even where the rumen is pretty well filled.

[Illustration:

FIG. 383.—FRONTAL SECTION OF KIDNEY OF OX.

_L_, Lobes of cortex; _P_, papillæ; _C_, calyx major; _c′_, calyces minores. ]

The kidneys are embedded in a large amount of perirenal fat. The weight of a kidney is about 20 to 25 ounces (ca. 570 to 700 gm.), the left one being usually an ounce or more the heavier. The two form about ¼ per cent. of the body-weight.

The right kidney measures about 8 to 10 inches (ca. 20 to 25 cm.) in length, 4 to 5 inches (ca. 10 to 12 cm.) in width, and 2½ to 3 inches (ca. 7 cm.) in thickness. The left kidney is one or two inches (ca. 2 to 5 cm.) shorter, but its posterior part is much thicker than the right one.

=Structure.=—The hilus is equivalent to the hilus and sinus of the kidney of the horse; in the right kidney it is an extensive elliptical cavity, in the left, a deep fissure. The pelvis is absent. The ureter begins at the junction of two wide, thin-walled tubes, the =calyces majores=; the anterior calyx is usually the larger. Each calyx major gives off a number of branches, and these divide into several funnel-shaped =calyces minores=, each of which embraces a renal papilla. The space not occupied by the calyces and vessels is filled with fat.

On section through the kidney the =renal pyramids= are easily made out. The blunt apex of each pyramid, the =papilla renalis=, projects into a calyx minor. On each papilla are small orifices (Foramina papillaria) by which the terminal renal tubules (Ductus papillares) open into the calyx. The renal columns are much more distinct than in the horse.

At the hilus the renal artery is dorsal, the vein in the middle, and the ureter ventral; a quantity of fat surrounds these structures in the hilus.

The kidneys of the =sheep= are bean-shaped and smooth, without any superficial lobation. The soft organ is regularly elliptical in form, with convex dorsal and ventral surfaces and rounded extremities; its length is about 2½ to 3 inches (ca. 5 to 8 cm.), its width about 1½ to 2 inches (ca. 4 to 5 cm.), and its thickness a little more than 1 inch (ca. 3 cm.). In position they resemble those of the ox, except that the right one is usually a little further back, and lies under the first three lumbar transverse processes. The average weight of each is about four ounces. The hilus is in the middle of the inner border. There is a renal crest or common papilla formed by the fusion of twelve to sixteen pyramids.

[Illustration:

FIG. 384.—KIDNEY OF SHEEP, VENTRAL VIEW.

_V.V._, Branches of renal vein. ]

[Illustration:

FIG. 385.—KIDNEY OF SHEEP, HORIZONTAL SECTION.

_1_, Cortical substance; _2_, medullary substance; _3_, renal crest; _4_, renal pelvis; _5_, ureter. (From Leisering’s Atlas, reduced.) ]

When the rumen is full, the left kidney (which is attached by a short mesentery) usually lies entirely to the right of the median plane, under the third, fourth, and fifth lumbar transverse processes. The primitive dorsal surface has become ventro-medial, and is somewhat flattened by contact with the rumen.

The =ureters= are, in general, like those of the horse, except in regard to the first part of the left one, which has a peculiar course, in conformity with the remarkable position of the kidney. It begins at the ventral part of the hilus (which faces toward the right), curves upward and inward over the outer aspect of the kidney to its dorsal surface, crosses the median plane, and runs backward on the left side.

The =bladder= is longer and narrower than that of the horse, and extends further forward on the abdominal floor. The peritoneal coat extends backward further than in the horse.

THE ADRENAL BODIES

The =right adrenal= lies against the inner part of the anterior pole of the right kidney. When hardened _in situ_ it is pyramidal in form. Its inner surface is flattened and is in contact with the right crus of the diaphragm. The outer surface is convex and lies in the renal impression of the liver. The ventral surface is grooved for the posterior vena cava; on this surface a relatively large vein emerges near the apex. The base is concave and rests obliquely against the anterior pole of the kidney. The apex fits into the angle between the posterior vena cava and the dorsal border of the liver.

The =left adrenal= lies on the inner face of the posterior vena cava just behind the anterior mesenteric artery, and is therefore practically median in position. It is flattened, and irregularly triangular or heart-shaped in outline. Its left face is related to the dorsal sac of the rumen. Its right face is related to the vena cava, and presents a large emergent vein. The posterior border or base is deeply notched.

[Illustration:

FIG. 386.—LEFT ADRENAL OF OX, VENTRAL VIEW: HARDENED _in situ_. ]

[Illustration:

FIG. 387.—RIGHT ADRENAL OF OX, VENTRAL VIEW: HARDENED _in situ_. ]

It is interesting to note that the left adrenal does not migrate with the kidney, but retains its primitive position; it lies usually about two inches (ca. 5 cm.) in front of a transverse plane through the anterior pole of the left kidney.

The adrenals of the =sheep= are both bean-shaped. The right one lies along the anterior part of the inner border of the kidney, at the angle of the junction of the right renal vein and the posterior vena cava. It is a little over an inch (ca. 3 cm.) long, and about an inch (ca. 12 to 15 mm.) wide. The left adrenal is longer, flatter, and somewhat bent. It lies across the left renal vein, to which it is attached, but is not in contact with the kidney.

[Illustration:

FIG. 388.—KIDNEYS OF PIG _in situ_, VENTRAL VIEW.

_C.a._, Hepatic artery; _M.a._, gastro-splenic artery. ]

[Illustration:

FIG. 389.—FRONTAL SECTION OF KIDNEY OF PIG. ]

URINARY ORGANS OF THE PIG

The =kidneys= are smooth and bean-shaped; they are more flattened dorso-ventrally, more elongated, and smaller at the extremities than those of the dog. The length is about twice the width. They are usually almost symmetrically placed on either side of the first four lumbar vertebræ. (Variations in position are not rare, and involve the left kidney oftener than the right. The former has been found near the pelvic inlet.) The external border lies against the flank parallel with the edge of the longissimus muscle. The posterior extremity usually lies about midway between the last rib and the external angle of the ilium. The anterior extremity of the right kidney usually extends as far forward as the last rib, but has no contact with the liver.

The weight of the kidney of a medium-sized pig is about seven to nine ounces (200 to 250 grams). The ratio of their combined weight to that of the body is about 1 ∶ 150–200.

=Structure.=—The hilus is about in the middle of the inner border. The pelvis is funnel-shaped, and divides into two calyces majores, which pass in a curve forward and backward respectively, and give off some eight to twelve short calyces minores; each of the latter contains a papilla. Some papillæ are narrow and conical, and correspond to a single pyramid; others are wide and flattened, and result from the fusion of two or more pyramids; some project directly through the wall of the pelvis without the formation of a calyx. The renal pyramids are distinct, but it is apparent that some are compound, _i. e._, formed by fusion of primitively separate pyramids. The renal artery enters the ventral part of the hilus, and the ureter leaves it dorsally.

The only special feature in regard to the =ureter= is that it is at first relatively wide and gradually diminishes in caliber.

The =bladder= is relatively very large; when full, it lies chiefly in the abdominal cavity. It is almost completely covered with peritoneum.

URINARY ORGANS OF THE DOG

The =kidneys= are relatively large, forming about ¹⁄₁₅₀ to ¹⁄₂₀₀ of the body-weight; the weight of the kidney of a medium-sized dog is about two ounces (ca. 50 to 60 grams). They are both bean-shaped, thick dorso-ventrally, with a rounded ventral surface and a less convex dorsal surface; the surfaces are smooth.

The =right kidney= (Fig. 343) is not subject to much variation in position; it is situated usually under the last rib and the first three lumbar transverse processes. Its anterior part lies in the deep renal impression of the liver; its posterior part is related to the sublumbar muscles dorsally, and the pancreas and duodenum ventrally.

The =left kidney= (Fig. 342) is subject to some variation in position; this is due to the fact that it is loosely attached by the peritoneum, and is affected by the degree of fullness of the stomach. When the stomach is nearly empty, the kidney usually lies under the transverse processes of the second, third, and fourth lumbar vertebræ, so that its anterior pole is opposite to the hilus of the right kidney. As the stomach fills it pushes the left kidney backward, so that the anterior pole of the latter may be opposite the posterior pole of the right kidney. The dorsal surface is related to the sublumbar muscles. The ventral surface is in contact with the terminal part of the colon (Colon descendens). The external border is related to the spleen and the flank. The anterior extremity touches the stomach and the left extremity of the pancreas.

The external border of the left kidney has considerable contact with the flank, and hence it may be palpated more or less distinctly in the living animal about half-way between the last rib and the crest of the ilium.

=Structure.=—The hilus is in the middle of the inner border and is, relatively wide. Cortex, limiting zone, and medulla are clearly defined. On frontal sections it is seen that the medullary substance forms a horizontal renal crest like that of the horse, but with the important difference that curved ridges proceed dorsally and ventrally from the crest somewhat like buttresses. Sections above or below the renal crest often cut these ridges in such a manner as to give the appearance of conical papillæ, and thus tend strongly to produce a false impression. The pelvis is adapted to this arrangement of the medullary substance. It incloses a central cavity into which the renal crest projects, and is prolonged outward between the ridges, forming cavities for the latter, thus simulating the appearance of calyces which do not exist.

The =ureters= present no special features.

The =bladder= is abdominal in position, the neck lying at the anterior border of the pubic bones. It is relatively large, and when full, the vertex may reach to the umbilicus. It has a practically complete peritoneal coat.

THE ADRENALS

The =right adrenal= lies between the anterior part of the inner border of the kidney and the posterior vena cava. It is somewhat prismatic, and is pointed at either end.

The =left adrenal= lies along the posterior aorta, from the renal vein forward, but is not in contact with the kidney. It is elongated and flattened dorso-ventrally. (There is a furrow on the ventral surface for the vein which crosses it; the part in front of this furrow is discoid, and may be taken for the entire organ in a fat subject.)

The cortex is pale yellow in color, the medulla dark brown.

THE MALE GENITAL ORGANS

The male =genital organs= (Organa genitalia masculina) are: (1) The two =testicles=, the essential reproductive glands, with their coverings and appendages; (2) the =vasa deferentia=, the ducts of the testicles; (3) the =vesiculæ seminales=; (4) the =prostate=, a musculo-glandular organ; (5) the two =bulbo-urethral= (or Cowper’s) =glands=; (6) the male =urethra=, a canal which transmits the generative and urinary secretions; (7) the =penis=, the male copulatory organ. The vesiculæ seminales, the prostate, and the bulbo-urethral glands discharge their secretions into the urethra, where they mix with the seminal fluid secreted by the testicles; hence they are often termed the accessory sexual glands.

MALE GENITAL ORGANS OF THE HORSE

THE TESTICLES