Part 50

The length of the =nasal cavity= varies greatly in different breeds, corresponding, of course, to the length of the face. The cavity is roomy, but is very largely occupied by the turbinals and the lateral masses of the ethmoid bone. The =middle meatus= is short and narrow, and divides posteriorly into two branches; the upper branch leads to the ethmoidal meatuses; the lower branch joins the inferior meatus. The =inferior meatus= is very small in its middle part, owing to the great development here of the inferior turbinal. The posterior part of the nasal cavity is divided by a horizontal plate, the lamina transversalis, into an upper olfactory part and a lower respiratory part. The sinuses have been described (_vide_ Osteology).

[Illustration:

FIG. 372.—NASAL CARTILAGES OF DOG.

_a_, Upper parietal cartilage; _b_, lower parietal cartilage; _c_, alar cartilage. (After Ellenberger, in Leisering’s Atlas.) ]

THE LARYNX

The larynx is relatively short. The lamina of the =cricoid cartilage= is wide; the arch is grooved laterally. The laminæ of the =thyroid cartilage= are high, but short; they unite ventrally to form the body, on which there is anteriorly a marked prominence, and posteriorly a deep notch. The oblique line on the outer surface of the lamina is prominent. There is a rounded notch (Fissura thyreoidea) below the short anterior cornua for the passage of the superior laryngeal nerve. The posterior cornu is strong, and has a rounded surface for articulation with the cricoid cartilage. The =arytenoid cartilages= are relatively small, and have between them a small =interarytenoid cartilage=. The =epiglottis= is quadrilateral; its lower part or stalk is narrow, fitting into the angle of the thyroid cartilage. The =cuneiform cartilages= are large and somewhat crescent-shaped; they are not blended with the epiglottis.

[Illustration:

FIG. 373.—SAGITTAL SECTION OF NASAL REGION OF DOG.

_1_, Skin; _2_, parietal cartilage; _3_, floor of nasal cavity; _4_, lamina transversalis; _5_, mucous membrane of hard palate; _6_, upper lip; _7_, frontal bone; _8_, frontal sinus; _9_, cranial plate of frontal bone; _10_, cranial cavity; _11_, dotted line indicating anterior limit of olfactory region; _a_, superior turbinal; _b_, inferior turbinal; _b′_, _b″_, inferior turbinal fold; _c_, _e_, ethmoturbinals; _d_, cribriform plate of ethmoid; _f_, superior meatus; _g_, middle meatus; _h_, inferior meatus; _i_, naso-pharyngeal meatus. (After Ellenberger, in Leisering’s Atlas.) ]

The =false vocal cords= extend from the cuneiform cartilages to the thyroid. The =true vocal cords= are large and prominent. The entrance to the large lateral ventricle and saccule is a long slit parallel with the anterior margin of the true vocal cord.

The crico-thyroid muscle is thick. The hyo-epiglotticus is well developed, and is double at its hyoid attachment. The anterior part of the thyro-arytenoideus arises on the cuneiform cartilage. Hence Lesbre has suggested the name cuneo-arytenoideus for it.

THE TRACHEA AND BRONCHI

The trachea is very slightly flattened dorsally. It contains forty to forty-five =U=-shaped rings; the ends of the rings do not meet dorsally, so that here the wall of the trachea is membranous and is composed of a layer of transverse smooth muscle-fibers outside of the rings, the fibrous membrane, and the mucous membrane.

The stem bronchi diverge at an obtuse angle, and each divides into two branches before entering the lung. The anterior branch goes to the apical and cardiac lobes, the posterior one to the diaphragmatic lobe, supplying also the mediastinal lobe of the right lung. The anterior branch of the left bronchus crosses under the pulmonary artery.

THE LUNGS

The lungs (Figs. 342, 343) differ in shape from those of the horse and ox in conformity with the shape of the thorax, which is relatively very wide in the dog; the lateral thoracic walls are strongly curved, and the costal surface of the lungs is correspondingly convex. There is no cardiac notch on the left lung, although a small part of the pericardium is not covered by the lung at the lowest part of the fifth and sixth intercostal spaces. On the right side the cardiac notch is opposite the fourth and fifth intercostal spaces. Each lung is divided by deep fissures into =three lobes=—=apical=, =cardiac=, and =diaphragmatic=; the right lung has in addition a =mediastinal lobe=. The apical lobe of the right lung is considerably larger than that of the left. The latter is often more or less fused with the cardiac lobe. Variable accessory lobes may be found. On account of the small amount of interlobular tissue the lobulation is not distinct.

THE THYROID GLAND

The =lateral lobes= of the thyroid gland are long and narrow, and have a flattened, ellipsoidal form; they are placed on the lateral surfaces of the trachea near the larynx. The extremities are small, the posterior one often being pointed. The =isthmus= is inconstant and variable; in large dogs it usually has the form of a glandular band which may be nearly half an inch (ca. 1 cm.) wide; in small dogs it is usually absent.

=Accessory thyroids= are frequently present; three or four may be found on either side, as well as a median one near the hyoid bone.

The =parathyroids=, about the size of millet or hemp seed, are four in number usually. Two are placed on the deep face of the thyroid lobes; the others are placed laterally near the anterior extremity of the thyroid.

THE THYMUS

The thymus is relatively small, and is situated almost entirely in the thorax. The left lobe is much larger than the right, and extends back as far as the sixth rib at the time of its greatest size. According to Baum the gland increases in size during the first two weeks after birth, and atrophies rapidly in the next two or three months. Traces of it are present at two or three years of age, and may be found even in old subjects.

THE UROGENITAL SYSTEM

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

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=.

[Illustration:

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 URINARY ORGANS OF THE HORSE

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.

[Illustration:

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. ]

[Illustration:

FIG. 376.—KIDNEYS AND ADRENALS OF HORSE, DORSAL VIEW.

Hardened _in situ_. Impression of seventeenth rib on right kidney is indicated by small cross. ]

[Illustration:

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 rightkidney. 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.

[Illustration:

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.

[Illustration:

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.

[Illustration:

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

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

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.