This system (Apparatus urogenitalis) includes two groups of organs, the urinary and the genital. The urinary organs elaborate and remove the chief excretory fluid, the urine. The genital organs serve for the formation, development, and expulsion of the products of the reproductive glands. In the higher vertebrates the two apparatus are independent except at the terminal part, which constitutes a urogenital tract, and includes the vulva in the female and the greater part of the urethra in the male.
The urinary organs (Organa uropoiëtica) are the kidneys, ureters, bladder, and urethra. The kidneys are the glands which secrete the urine; they are red-brown in color, and are situated against the dorsal wall of the abdomen, being in most animals almost symmetrically placed on either side of the spine. The ureters are tubes which convey the urine to the bladder. The latter is an ovoid or pyriform sac, situated on the pelvic floor when empty or nearly so; it is a reservoir for the urine. The urine accumulates in the bladder until that organ is full, and is then expelled through the urethra.
Fig. 374.—General Dorsal View of Urinary Organs of Horse.
1, Right kidney; 1′, left kidney; 2, 2′, adrenal bodies; 3, 3′, ureters; 4, urinary bladder; 4′, anterior end of bladder with cicatricial remnant of urachus; 4″, urethra; 5, aorta; 6, 6, renal arteries; 7, 7, external iliac arteries; 8, 8, internal iliac arteries; 9, 9, umbilical arteries. (After Leisering’s Atlas.)
THE KIDNEYS
Each kidney (Ren) presents two surfaces, two borders, and two extremities or poles, but they differ so much in form and position as to require a separate description of each in these respects.[135]
The right kidney (Ren dexter) in outline resembles the heart on a playing card, or an equilateral triangle with the angles rounded off. It lies ventral to the upper parts of the last two or three ribs and the tip of the first lumbar transverse process. The dorsal (or superior) surface (Facies dorsalis) is strongly convex; it is related chiefly to the diaphragm, but also to a small extent posteriorly to the psoas muscles. In well hardened specimens, especially those from thin subjects, impressions of the last two ribs and the tip of the first lumbar transverse process are usually visible. The ventral (or inferior) surface (Facies ventralis) is in general slightly concave, and is related to the liver, pancreas, cæcum, and right adrenal; it either has no peritoneal covering, or only a narrow area externally is so covered. The internal border (Margo medialis) is convex and rounded; it is related to the right adrenal and the posterior vena cava. It presents about its middle a deep notch, the hilus (Hilus renalis); this is bounded by rounded margins, and leads into a space termed the renal sinus (Sinus renalis). The vessels and nerves reach the kidney at the hilus, and the sinus contains the pelvis or dilated origin of the ureter. The external border (Margo lateralis) is rounded, and is thinner than the internal one. It consists of two parts, anterior and posterior, which meet at an external angle; the anterior part fits into the renal impression of the liver. The duodenum curves around the external border. The anterior extremity (Extremitas cranialis), thick and rounded, lies in the renal impression of the liver. The posterior extremity (Extremitas caudalis) is thinner and narrower.
Fig. 375.—Diagram of Position and Dorsal Relations of Kidneys of Horse.
Areas of direct relations are inclosed by continuous lines; parts of skeleton which overlie the kidneys but are not in contact with them are indicated by dotted lines. L.I-III, lumbar transverse processes.
Fig. 376.—Kidneys and Adrenals of Horse, Dorsal View.
Hardened in situ. Impression of seventeenth rib on right kidney is indicated by small cross.
Fig. 377.—Kidneys and Adrenals of Horse, Ventral View.
Hardened in situ. Left renal vein (not marked) is seen curving round posterior end of left adrenal.
The left kidney (Ren sinister) is bean-shaped. It is considerably longer and narrower than the right one, and is situated nearer the median plane and further back, so that the hilus of the left kidney is about opposite to the posterior extremity of the right one. It lies usually under the upper part of the last rib and the first two or three lumbar transverse processes. The dorsal surface is convex, and is related to the left crus of the diaphragm, the psoas muscles, and the base of the spleen. The ventral surface is convex and irregular; the greater part of it is covered by the peritoneum. It is in relation with the origin of the small colon, the terminal part of the duodenum, the left adrenal, and the left extremity of the pancreas. The internal border is longer, straighter, and thicker than that of the right kidney. It is related to the posterior aorta, the adrenal, and the ureter. The external border is related chiefly to the base of the spleen. The anterior extremity extends almost to the saccus cæcus of the stomach; it is related to the left end of the pancreas, and the splenic vessels. The posterior extremity is usually larger than the anterior one.
The form of the left kidney is variable. In some cases its outline is similar to that of the right kidney, but its ventral surface is convex and is often marked by several furrows which diverge from the hilus. In well hardened specimens the three areas of the dorsal surface are often distinct. The psoas area is flat, parallel with the inner border, and widens behind. The diaphragmatic area is small and convex; it is crescentic and is confined to the anterior pole. The splenic area, convex and external, is often so extensive and distinct as really to constitute a third surface.
Fixation.—The kidneys are held in position chiefly by the pressure of adjacent organs and by the renal fascia. The latter is a special development of the subperitoneal tissue, which splits into two layers to inclose the kidney, together with the perirenal fat or capsula adiposa. On account of its relations with the liver, pancreas, and the base of the cæcum, the right kidney is much more strongly attached than the left one. It is, therefore, not surprising that the latter varies somewhat in position; its posterior pole may be found ventral to the third or fourth lumbar transverse process. The position of the right kidney seems to be very constant, excluding its movements during respiration.
Fig. 378.—Frontal (Horizontal) Section of Kidney of Horse.
The renal vein is removed. A large accessory renal artery entered the posterior pole. Sections of arteries in limiting layer between cortical and medullary substance are white in figure.
Weight and Size.—The right kidney is usually one or two ounces heavier than the left. The average weight of the right kidney is about 23 to 24 ounces (ca. 700 gm.); that of the left, about 22 to 23 ounces (ca. 670 gm.). The relation of the weight of both kidneys to the body-weight is about 1 ∶ 300–350.
Chauveau gives as an average 750 grams for the right kidney, and 710 grams for the left. Ellenberger and Baum (24 cases) give the right kidney as varying between 430 and 840 grams; and the left between 425 and 780; this is an average of 635 grams (about 22½ ounces) for the right kidney, and 602.5 grams (about 21½ ounces) for the left. They give the relation of the weight of both kidneys to the body-weight as 1 ∶ 255–344. In a Percheron mare weighing about 2000 pounds the right kidney weighed 4 pounds 3 ounces, and the left one 4 pounds. In a horse of medium size the right kidney is about six inches (ca. 15 cm.) in length, about the same in width, and about two inches (ca. 5 cm.) thick. The left kidney is about seven inches (ca. 18 cm.) long, four to five inches (ca. 10 to 12 cm.) wide, and two to two and a half inches (ca. 5 to 6 cm.) thick.
Structure.—The surface of the kidney is covered by a thin but strong fibrous capsule (Tunica fibrosa), which is in general easily stripped off the healthy kidney. It is continued along the hilus and lines the renal sinus. Sections through the kidney show it to consist of an external cortical substance and an internal medullary substance.[136] The cortical substance (Substantia corticalis) is red brown in color and has a granular appearance. It is dotted over with minute dark points; these are the renal (or Malpighian) corpuscles (Corpuscula renis), each consisting of the dilated origin of a uriniferous tubule (Capsula glomeruli), with an invaginated tuft of capillaries (Glomerulus) inclosed by it. The medullary substance (Substantia medullaris) is more resistant and presents a distinct radial striation. Its central part is pale, but its periphery, the intermediate zone, is of a deep red color; in the latter are seen, at fairly regular intervals, sections of the relatively large arciform vessels, which are taken to represent the demarcation between the primitive lobes.[137] Between the vessels the medulla is prolonged somewhat toward the periphery, forming the bases of the renal (or Malpighian) pyramids. These are not very pronounced in the kidney of the horse, especially as the gland is not papillated. Between the bases of the pyramids processes of the cortex dip in toward the sinus, forming the renal columns.[138] The inner central part of the medulla forms a concave ridge or crest which projects into the pelvis of the kidney; the crest is marked by numerous small openings at which the renal tubules terminate.
Fig. 379.—Transverse Section of Right Kidney of Horse Through the Hilus.
Posterior portion of organ hardened in situ. Note curvature of dorsal surface.
Examination with a pocket lens shows that the cortex is imperfectly divided into lobules (Lobuli corticales). Each lobule consists of an axial radiate part (Pars radiata), surrounded by a convoluted part (Pars convoluta). The former (formerly termed pyramids of Ferrein) appear as ray-like prolongations from the bases of the pyramids (hence also termed medullary rays), and consist largely of narrow, straight or slightly flexuous, tubules (limbs of the loops of Henle). The convoluted part (formerly termed the labyrinth) is granular in appearance, and consists largely of the renal corpuscles and convoluted tubules.
The pelvis of the kidney (Pelvis renalis) is the dilated origin of the excretory duct. It lies in the sinus of the kidney, and it is funnel-shaped, but flattened dorso-ventrally. The renal crest[139] (Papilla communis) projects into the outer part of the pelvis in the form of a horizontal ridge with a concave free edge. The tubules of the middle part of the medullary substance open on this crest into the pelvis. The tubules from each end of the kidney do not open into the pelvis proper (Recessus medius), but into two long, narrow diverticula (Recessus terminales), which proceed from it toward the poles of the kidney. The wall of the pelvis consists of three layers. The external fibrous coat or adventitia is continuous with the supporting tissue of the kidney. The muscular coat consists of longitudinal and circular fibers. The mucous coat does not cover the renal crest, nor is it continued into the diverticula of the pelvis. It has a yellowish tinge, and presents numerous folds. It contains glands (Glandulæ pelvis renalis) which secrete the thick mucus always found in the pelvis.
Fig. 380.—Diagrammatic Scheme of Uriniferous Tubules and Blood-vessels of Kidney.
Drawn in part from the descriptions of Golubew (Böhm, Davidoff, and Huber).
Renal Tubules—The parenchyma or proper substance of the kidney is composed of the small renal or uriniferous tubules (Tubuli renales), which are very close together and have a complicated course. Each tubule begins in a thin-walled, spherical dilatation or capsule, which is invaginated to receive a tuft of looped capillaries termed a glomerulus; these two structures constitute a renal (or Malpighian) corpuscle; the corpuscles are visible as minute red or dark spots in the convoluted part of the cortex. Succeeding this is a short narrow neck, beyond which the tubule becomes wide and convoluted, forming the proximal convoluted tubule, and enters the radiate portion of the cortex. It then gradually narrows and enters the intermediate zone; becoming very narrow and nearly straight, it descends for a variable distance into the medullary substance, turns sharply upon itself, and returns to the cortex, forming thus the loop of Henle, with its descending and ascending limbs. In the convoluted part of the cortex, it widens and becomes tortuous, constituting the distal convoluted tubule. The tubule then narrows, enters a medullary ray, and opens with other tubules into a straight collecting tubule; this passes axially through a pyramid, and unites with other collecting tubules to form the relatively large papillary ducts, which open into the renal pelvis.
Stroma.—The interstitial tissue forms a reticulum throughout which supports the tubules and blood-vessels. It is very scanty in the cortex, much more abundant in the medulla, in which it increases in amount toward the pelvis.
Blood-supply.—The kidneys receive a large amount of blood through the renal arteries. Branches of these enter at the hilus and on the ventral surface of the gland, and reach the intermediate zone, where they form anastomotic arches (Arteriæ arciformes). From these arciform arteries branches pass into the cortex and medulla. The cortical branches (Arteriæ interlobulares) have in general a radial course between the cortical lobules, and give off short lateral branches, each of which ends as the afferent vessel (Vas afferens) of a renal corpuscle. The blood is carried from the glomerulus by a smaller efferent vessel, which breaks up immediately into capillaries which form networks around the tubules. The medullary branches descend in the pyramids, forming in them bundles of straight twigs (Arteriolæ rectæ).
The veins correspond in general to the arteries. In the superficial part of the cortex the veins form star-like figures (Venæ stellatæ) by the convergence of several small radicles to a common trunk.
Lymph Vessels.—These may be divided into two sets, capsular or superficial, and parenchymatous or deep.
Nerve-supply.—The nerves are derived from the renal plexus of the sympathetic, and form a plexus around the vessels.
The ureters are the narrow part of the excretory ducts of the kidneys. Each begins at the renal pelvis and terminates at the bladder. It is about ⅓ to ¼ inch (ca. 6 to 8 mm.) in diameter, and its average length is about 28 inches (ca. 70 cm.). The abdominal part (Pars abdominalis) of each ureter emerges ventrally from the hilus of the kidney, and curves backward and inward toward the lateral face of the posterior vena cava (right side) or the posterior aorta (left side). They then pass almost straight backward in the subperitoneal tissue on the surface of the psoas minor, cross the external iliac vessels, and enter the pelvic cavity. The pelvic part (Pars pelvina) passes backward and a little downward on the lateral wall of the pelvic cavity, turns inward, and pierces the dorsal wall of the bladder near the neck.
In the male the pelvic part enters the urogenital fold and crosses the vas deferens. In the female the ureter is situated in the greater part of its course in the dorsal part of the broad ligament of the uterus.
The wall of the ureter is composed of three coats. The outer fibrous coat (Tunica adventitia) is composed of loose fibrous tissue. The muscular coat (Tunica muscularis) consists of inner and outer layers of longitudinal fibers, with a stratum of circular fibers between them. The mucous membrane (Tunica mucosa) is covered with transitional epithelium; glands (Glandulæ mucosæ ureteris) resembling those of the renal pelvis occur in the first three or four inches of the ureter.
The urinary bladder (Vesica urinaria) (Figs. 270, 271, 272) differs in form, size, and position according to the amount of its contents. When empty and contracted, it is a dense, pyriform mass, about the size of a fist, lies on the ventral wall of the pelvic cavity, and does not reach to the inlet. When moderately filled, it is ovoid in form, and extends a variable distance along the ventral abdominal wall. Its physiological capacity varies greatly, but may be estimated approximately at about three or four quarts.
The anterior rounded blind end is termed the vertex;[140] on its middle is a mass of cicatricial tissue (Centrum verticis), a vestige of the urachus, which in the fœtus forms a tubular connection between the bladder and the allantois. The body or middle part (Corpus vesicæ) is rounded, and is somewhat flattened dorso-ventrally, except when distended. It presents two surfaces, dorsal and ventral, the former being the more strongly convex, especially in its posterior part in front of the entrance of the ureters.[141] The posterior narrow extremity, the neck (Collum vesicæ), joins the urethra.
The relations of the bladder vary according to the degree of fullness of the organ, and also differ in important respects in the two sexes. The ventral surface lies on the ventral wall of the pelvis, and extends forward on the abdominal wall as the bladder fills. The dorsal surface in the male is related to the rectum, the urogenital fold, the terminal parts of the vasa deferentia, the vesiculæ seminales, and the prostate; in the female it is in contact, instead, with the body of the uterus and the vagina. The vertex of the full bladder is related to coils of the small intestine and small colon, and to the pelvic flexure of the large colon.
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 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.
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.)
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.
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.
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.
Fig. 384.—Kidney of Sheep, Ventral View.
V.V., Branches of renal vein.
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 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.
Fig. 386.—Left Adrenal of Ox, Ventral View: Hardened in situ.
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.
Fig. 388.—Kidneys of Pig in situ, Ventral View.
C.a., Hepatic artery; M.a., gastro-splenic artery.
Fig. 389.—Frontal Section of Kidney of 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.
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 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.