Anatomy of the Cat

by Jacob Reighard; H. S. Jennings

IV. THE UROGENITAL SYSTEM. APPARATUS UROGENITALIS.

1. The Excretory Organs.

Kidney. Ren

([Figs. 108] and [109]).

[Fig. 108].—Left Kidney, Ventral Surface.

[Fig. 109].—Median Longitudinal Section of Kidney.

Fig. 108.—a, renal artery; b, renal vein; c, ureter.

Fig. 109.—a, medullary portion; b, cortical portion; c, papilla; d, pelvis; e, renal artery; f, renal vein; g, ureter.

The kidneys of the cat are compact (i.e., not lobulated) and have the usual kidney or bean form. They lie in the abdominal cavity, one on either side of the vertebral column, against the dorsal body wall, in the region between the third and fifth lumbar vertebræ. The right kidney is one or two centimeters farther craniad than the left, and the long axes of the two converge craniad a little. Each is covered by peritoneum on its ventral surface only (i.e., it is retroperitoneal). At the border of the kidney, where the peritoneum passes from it to the body wall, there is an accumulation of fat, which is most abundant at the cranial end of the kidney. Within the peritoneal investment the kidney is enclosed in a special loose fibrous covering, the capsule or tunica fibrosa, which is continuous with the fibrous coat of the ureter and pelvis. In the middle of the median border of each kidney is a notch, the hilus. It gives exit to the ureter ([Fig. 108], c) and renal veins (b), and entrance to the renal artery (a). On the ventral surface of the kidney within the capsule are seen grooves radiating from the hilus. They contain blood-vessels. If the substance of the kidney is sliced away parallel to the ventral surface for some distance ([Fig. 109]), there is exposed a cavity, the sinus, which lies near the medial border and the opening of which is the hilus. It contains the pelvis (d) (the expanded beginning of the duct of the kidney), and also renal vessels (e and f) with their branches. These structures are enclosed in fat, which fills the remainder of the sinus. Upon opening the pelvis the kidney substance is seen to project into it in the form of a cone, the papilla (c), the apex of which is directed mediad. On the apex of the papilla are the numerous openings of the uriniferous collecting-tubes, some of them opening at the bottom of an apical depression of the papilla.

In a section made parallel to the ventral surface and in the median plane, the substance of the kidney is seen to consist of a peripheral darker and more granular cortical portion ([Fig. 109], b), and of a central, lighter, less granular medullary portion (a). Both portions are marked by lines which converge to the apex of the papilla (c).

The Ureter

([Fig. 108], c; [Figs. 111] and [112], b).—The duct of the kidney begins as the pelvis ([Fig. 109], d), a conical sac the base of which encloses the base of the papilla. From the apex of the papilla the urine passes into the pelvis. The outer wall of the pelvis is continuous with the capsule of the kidney. At the hilus the pelvis narrows to form the ureter ([Fig. 109], g). The ureter passes caudad in a fold of peritoneum which contains fat. Near its caudal end it passes dorsad of the vas deferens ([Fig. 111], c), turns ventrocraniad, and pierces the dorsal wall of the bladder ([Fig. 111], a) obliquely near the neck. On the inside of the bladder the openings of the ureters appear as pores about five millimeters apart, and each is surrounded by a white, ring-like elevation of the surface.

The Bladder. Vesica urinaria.

—The bladder ([Fig. 111], a) is pear-shaped. It lies in the abdominal cavity between its ventral wall and the rectum and a short distance craniad of the pubic symphysis. Caudad it is continued into a rather long, narrow neck (f) which passes dorsad of the symphysis to the pelvic cavity.

The bladder is covered by peritoneum and is held in place by its neck and by three folds of the peritoneum. One of these passes from its ventral wall to the linea alba and is the suspensory ligament. Two others pass one from each side of the bladder to the dorsal body wall at the sides of the rectum. They are the lateral ligaments of the bladder. They form the walls of a partly isolated peritoneal pocket into which the rectum passes; this pocket opens craniad into the peritoneal cavity. The wall of the bladder is composed of an internal epithelium, a layer of plain muscle-fibre bundles which cross one another in various directions, and the external peritoneal layer.

Suprarenal Bodies. Glandulæ suprarenales.

—The suprarenal bodies are two ovoid bodies about a centimeter in the longest diameter, lying craniomediad of the kidneys, but usually not touching them. In a fresh condition they are of a pinkish or yellow color. They are usually imbedded in fat and are covered by peritoneum on their ventral surface. They have no duct and are of uncertain function.

2. The Genital Organs.

A. The Male Genital Organs.

External Genital Organs.—The external genital organs are the scrotum and penis.

The scrotal sac or scrotum is a pouch of integument which lies ventrad of the anus in the median line against the ischiatic symphysis. It is marked by a median groove which indicates the position of an internal septum dividing its cavity into lateral halves, within each of which is one of the testes.

The penis ([Fig. 111], l; [Fig. 113], 6; see also [page 262]) lies ventrad of the scrotal sac. It projects caudad. It is covered by the integument, which projects at its end as a free fold, the prepuce. Within the prepuce is the projecting glans penis ([Fig. 113], 7). It is conical and bears on the ventral side of its free end the opening of the urethra, the common urinogenital opening. On the side on which the urethra opens the glans is connected to the prepuce by a fold of integument, the frenulum. The surface of the glans is covered with sharp, recurved, horny papillæ.

The Scrotum and Testes, and the Ducts of the Testes.—The scrotum contains the two testes, one in each of its compartments. Each testis lies in a diverticulum of the abdominal cavity, which is lined by an extension of the peritoneum. The testis has the same relation to this peritoneal diverticulum that the intestine has to the abdominal cavity; i.e., it does not lie within the cavity of the diverticulum, but is suspended apparently within it by means of a fold of its wall which acts as a mesentery. The peritoneal diverticulum is called the tunica vaginalis propria and consists thus of a parietal layer and a visceral layer.

The tunica vaginalis propria consists of a slender proximal part through which the blood-vessels pass to the testis and the vas deferens from it, and of an expanded distal part in which lies the testis. Only the distal part lies within the scrotum. The blood-vessels and vas deferens are suspended in the narrow part of the tunica vaginalis propria by means of a mesenterial fold similar to that which suspends the testis, and continuous with it. This fold and the blood-vessels and vas deferens contained within it form the spermatic cord ([Fig. 111], d) which passes from the abdomen to the scrotal sac in the narrow part of the tunica vaginalis propria. In the formation of the human tunica vaginalis the various layers of the body wall are carried out by it and form the tunics, or coats of the testis. The one of these coats next the tunica vaginalis propria (which is reckoned as one of the coats) is the tunica vaginalis communis (or fascia propria) and is formed by the transversalis fascia. Outside of the tunica vaginalis communis is the cremaster muscle, an incomplete layer formed from the fibres of the internal oblique muscle. Next is the cremasteric (or intercolumnar) fascia from the aponeurosis of the external oblique muscle, and outside of this is the integument forming the scrotum. In this integument there is a layer of smooth muscle which is sometimes described as the tunica dartos. In the cat the tunica dartos and the cremaster muscle are wanting. The cremaster is replaced by the elevator scroti muscle. The coats of the testis are thus five, as follows:

1. The scrotum (the integument).

2. Cremasteric fascia (subcutaneous fascia).

3. The levator scroti muscle (subcutaneous muscle-layer) ([Fig. 113], j).

4. Tunica vaginalis communis (transversalis fascia).

5. Tunica vaginalis propria (peritoneum).

The tunica vaginalis communis is inseparably united with the parietal layer of the tunica vaginalis propria. Where the spermatic cord passes from the abdominal wall to the scrotum it is covered by integument and cremasteric fascia on its ventral surface only, but is entirely surrounded by the tunica vaginalis propria and tunica vaginalis communis. The canal by which the spermatic cord passes through the body wall is known as the inguinal canal. The end by which it opens into the abdominal cavity is the internal inguinal ring, and the opposite end is called the external inguinal ring.

The internal inguinal ring is merely the point of connection between the proximal tubular portion of the tunica vaginalis propria and the abdominal cavity. It is circular, and is situated close against the lateral side of the lateral ligament of the bladder at its middle.

The external inguinal ring is an oval opening in the aponeurosis of insertion of the external oblique muscle. The aponeurosis of this muscle ends caudally in a free border along the cranial edge of the pubis, from the ilium to the pubic tubercle. The external ring is just craniad of the end of this aponeurosis.

The inguinal canal between these rings lies along the lateral border of the rectus muscle. It is one to one and a half centimeters long. Its medial wall rests on the rectus muscle; its dorsal wall on the fat contained within the lateral ligament of the bladder. The lateral and ventral walls lie on the transversus muscle proximally, on the internal oblique near the distal end. The wall itself is composed of tunica vaginalis propria and communis. As it passes within the caudal border of the internal oblique muscle it receives some aponeurotic fibres from it. A thin aponeurosis is also continued from the border of the external ring onto the tunica vaginalis propria.

[Fig. 110].—Testis.

a, testis; b, caput epididymis; c, epididymis; d, cauda epididymis; e, vas deferens; f, spermatic cord.

The testes ([Fig. 110]) are the organs which produce the spermatozoa. They lie one in each compartment of the scrotal sac, enveloped in the membranes or tunics [described] when treating of the scrotum. Each is attached to the dorsal wall of its peritoneal pouch by a mesenteric fold. The testis is surrounded by the visceral layer of the tunica vaginalis propria, and within this, by a dense fibrous covering, the tunica albuginea, which sends septa into its interior. Within the fibrous covering it is made up of numerous coils of seminiferous tubules which are readily seen by the naked eye.

The epididymis ([Fig. 110], c) is the beginning of the efferent duct of the testis. It appears as a flat band with a broad rounded end which lies on the medial surface of the testis at its cranial end (b). From this point it passes about the cranial end of the testis from its medial to its lateral surface, forming thus a semicircle with the convexity ventrad. Thence it passes as a narrower band (c) along the dorsal side of the testis, laterad of the suspending mesentery, to the caudal end of the testis (d). At the caudal end of the testis it is enlarged, passes from its lateral to its medial surface, and turns at the same time craniad to become continuous with the vas deferens (e).

The enlarged cranial end is the caput epididymis (b); the enlarged caudal end the cauda epididymis (d). The whole epididymis is encased in a tough fibrous covering similar to that of the testis. The fibrous covering (albuginea) of the testis and that of the epididymis are connected by fibrous tissue. Within the fibrous covering the head of the epididymis is made up of tubules which pass from the testis into its end: these are the vasa efferentia testis. The vasa efferentia unite within the caput into a single vessel which passes in a very tortuous course to the cauda. Its numerous windings form the cauda, from the end of which it passes craniad as the vas deferens (e).

The vas deferens ([Fig. 110], e; [Fig. 111], c) is a slender tube much convoluted at its beginning. It passes from the cauda epididymis (d) along the mesenterial fold of the testis on its medial side, to the spermatic cord ([Fig. 111], d). It leaves the spermatic cord at the internal inguinal ring and, curving over the ureter ([Fig. 111], b), bends craniad and approaches the vas deferens of the opposite side dorsad of the neck of the bladder ([Fig. 111], f). The two vasa deferentia pass caudad together as far as the cranial border of the pubis. There they enter the prostate gland (g), pierce the dorsal wall of the neck of the bladder, and open close together on the inner surface. The two openings are separated by a slight elevation, the veru montanum.

The Urethra ([Fig. 111], h).—The urethra is the common urinogenital duct which is formed by the union of the neck of the bladder (f) and the vasa deferentia (c) dorsad of the cranial border of the pubis. It extends thence to the end of the penis. It is divided into three portions.

1. The prostate portion is the commencement of the urethra; it is surrounded by the prostate gland (g).

2. The membranous portion (h) extends from the prostate portion to a point between the crura of the penis. This portion is surrounded by the thick compressor urethræ muscle, so that its wall appears much thicker than it really is.

3. The spongy portion (pars cavernosa) extends along the ventral side of the penis to its end in the groove between the corpora cavernosa penis. At its beginning is an enlargement formed by the bulbocavernosus muscle. This is known as the bulbus urethræ. The walls of the spongy portion are thick and vascular and form the corpus cavernosum urethræ or corpus spongiosum. At its end the corpus cavernosum urethræ is greatly enlarged and forms the glans penis (m).

Glands of the Urethra.—1. The prostate ([Fig. 111], g) is a bilobed gland lying on the dorsal wall of the urethra and surrounding the ends of the vasa deferentia (c). It opens into the urethra at its beginning by numerous small ducts visible to the naked eye on the inner surface of the urethra.

2. The bulbourethral or Cowper’s glands ([Fig. 111], i).—There are two bulbourethral or Cowper’s glands, one on either side of the bulbus of the urethra between the ischiocavernosus and bulbocavernosus muscles. Each has a covering of muscle-fibres derived from the neighboring bulbocavernosus ([Fig. 113], l). Each is said to open by a single duct into the urethra at the root of the penis.

Fig. 111.—Male Genital Organs.

a, bladder; b, b′, ureters; c, vasa deferentia; d, spermatic cord; e, spermatic artery and vein; f, neck of bladder; g, prostate gland; h, urethra; i, bulbourethral (or Cowper’s) gland; j, corpus cavernosum penis, cut from ischium; k, ischiocavernosus muscle (cut); l, penis; m, glans penis; n, testis.

The penis ([Fig. 111], l; [Fig. 113], 6) is a cylindrical organ with the apex directed backward. It is covered by integument which projects at its free end in the form of a fold, the prepuce ([Fig. 113]), which ensheaths the glans ([Fig. 113], 7) of the penis. Beneath the integument is a layer of strong fibrous subcutaneous fascia continuous with that of the surrounding parts. On the dorsum of the penis a thin band of fibrous tissue, the ligamentum suspensorium penis, is continued from the middle line beneath the pelvic symphysis. This band divides distally, and its halves ensheath the glans and thus form a support of the penis.

The penis is formed by three bodies, the two corpora cavernosa penis and the single corpus cavernosum urethræ (corpus spongiosum).

The corpora cavernosa penis ([Fig. 111], j). Each is a cylindrical sheath of dense fibrous tissue within which are trabeculæ separating blood-sinuses. Each corpus cavernosum is attached by the one pointed end to the caudal border of the ramus of the ischium near the symphysis. From their attachments the corpora cavernosa approach one another, forming the crura of the penis. They become closely united by their medial surfaces and pass thus to the free end of the penis where their somewhat pointed distal ends are imbedded in the glans (m). A groove is left between the corpora cavernosa on the dorsum of the penis, and there is a second groove on the ventral side. In the latter groove lies the urethra.

The corpus cavernosum urethræ is the spongy portion of the urethra which lies in the groove on the ventral surface of the penis, between the corpora cavernosa penis. It becomes greatly enlarged at the distal end of the penis, forming the glans (m). A small bone (os penis) is imbedded in the distal end of the penis.

B. Female Genital Organs

([Fig. 112]).—The urinal organs of the female are like those of the male. The neck (k) of the bladder is, however, much longer, extending almost to the border of the ischiatic ramus. The urethra is consequently short.

The genital organs consist of the ovaries (c) (the organs which produce the eggs), the oviducts or uterine tubes (e) (Fallopian tubes), which receive the eggs from the ovaries; a bifid uterus (f and i) in which the ova undergo their development, and a vagina (m) which leads from the uterus to its junction with the neck of the bladder.

The neck of the bladder (k) unites with the vagina to form the urogenital sinus (n) which is very short, leads to the external opening, and is comparable to the male urethra. Ventrad of the external orifice of the urogenital sinus is the clitoris, a rudimentary structure homologous with the penis of the male.

The Ovaries (c).—The ovaries lie in the abdominal cavity in the same longitudinal line with the kidneys and a short distance caudad of them. Each is an ovoid body about one centimeter long and one-third to one-half as broad. On its surface are numerous whitish projecting vesicles, the larger of which show clear centres. They are the Graafian follicles (best seen in section), which contain the eggs. There may be present one or more elevations of the size of the largest Graafian follicles, but of a bright red or brown color. They are the corpora lutea (sing. corpus luteum),—Graafian follicles from which the eggs have been discharged.

The ovary is held in position by the broad ligament of the uterus, a fold of the peritoneum, which passes here from the uterine tube to the adjacent body wall. The ovary lies in a sort of a pocket formed by the broad ligament. In the natural position the pocket opens ventrolaterad. The ovary is further held in position by the ligament of the ovary (ligamentum ovarii), a short thick cord which passes from the ventral face of the ovary at its uterine end to the adjacent ventral surface of the uterus.

The Uterine Tubes (e).—The uterine (or Fallopian) tubes or oviducts are the tubes which convey the ova from the ovary (c) to the uterus (f). Each begins with an expanded trumpet-shaped opening, the ostium tubæ abdominale (d). Its walls are thin, and the mucosa of its inner surface is thrown up into undulating, radiating ridges.

The ostium (d) lies on the lateral side of the ovary (c) at its cranial end, and the trumpet partly clasps the ovary. From the ostium the tube (e) turns craniad, then mediad, and then caudad, so as to describe a curve about the cranial end of the ovary. It then extends caudad on the mediodorsal aspect of the ovary to its junction with the uterine cornu (f). It is sinuous throughout its course, and the first two-thirds (the vestibulum) is of considerably greater diameter than the last third. Throughout the last two-thirds of its course it lies in the free border of the broad ligament. Its mucosa is thrown into irregular folds, mostly longitudinal, and is lined by ciliated epithelium. From the foregoing description it is seen that the ova must pass through the body cavity in order to reach the ostium tubæ.

[Fig. 112].—Female Urogenital Organs, Obliquely Ventral View.

a, kidney; b, ureter; c, ovary; d, ostium tubæ abdominale; e, uterine (Fallopian) tube; f, cornua of the uterus; g, cranial edge of broad ligament; h, round ligament of the uterus; i, body of the uterus; j, bladder; k, neck of the bladder; l, position of cervix uteri; m, vagina; n, urogenital sinus or vestibule, with M. urethralis; o, corpus cavernosum clitoridis, with M. ischiocavernosus (cut); p, fibres of M. constrictor vestibuli. 1, aorta; 2, internal spermatic arteries; 3, uterine arteries; 4, external iliac arteries; 5, hypogastric arteries; 6, umbilical artery; 7, inferior hemorrhoidal artery; 8, branches of N. pudendus.

The Uterus (f, i).—The uterus consists of a median portion or body (i) which is unpaired, and of two horns or cornua (f) which extend from the body to the uterine tubes. The body (i) of the uterus is a tube about four centimeters long which lies in the abdominal cavity, ventrad of the rectum and between it and the bladder. Its caudal end is at the level of the cranial border of the pubis. The cranial end of its cavity is divided by a median dorsoventral partition into lateral halves, while the cavity of its caudal portion is unpaired. The mucosa is thrown up into large longitudinal folds. At its caudal end the uterus projects into the vagina (m), so that when the vagina is opened the end of the uterus is seen projecting into it as a prominent papilla. The portion of the uterus thus enclosed by the vagina is the cervix uteri or neck of the uterus. Its free end is directed ventrocaudad, and a prominent ridge is continued from its caudodorsal side along the mid-dorsal wall of the vagina. The uterine cavity communicates with the vaginal cavity by a V-shaped opening, the os uteri, which looks ventrocaudad and has its apex directed cranioventrad. Each horn (f) of the uterus passes craniolaterad in a nearly straight course from the body (i) to the uterine tube (e). It narrows rapidly and becomes continuous with the tube. The mucosa is thrown into longitudinal folds.

Ligaments of the Uterus.—The Broad Ligament.—The uterus is held in place principally by the broad ligaments. These are two folds of the peritoneum, each of which is attached to the whole length of one of the cornua and the adjacent part of the uterine tube and to the corresponding lateral surface of the body of the uterus. Each ligament ends craniad in a concave free border. Its attached border forms a curved line which begins laterad of the kidney and extends thence to the lateral ligament of the bladder. From the lateral ligament of the bladder the broad ligament extends caudad into the rectovesical pouch of the peritoneum, which lies between the rectum and the bladder. It holds the body of the uterus to the lateral wall of this pouch, and together with the opposite ligament and the body of the uterus forms thus a transverse partition, which divides the rectovesical pouch into dorsal and ventral portions.

The round ligament (h) is a fibrous band which extends from a point of the body wall, which corresponds exactly to the internal inguinal ring of the male, to the cornu of the uterus about two centimeters from the cranial end. It is attached to the broad ligament by an intervening fold of peritoneum.

The Vagina (m).—The vagina extends from the os uteri (at l) dorsad of the symphysis of the pelvis to a point a short distance craniad of the caudal border of the ischiatic symphysis. At this point it joins the neck of the bladder (k) to form the vestibulum or urogenital sinus (n), which is homologous with the urethra of the male.

Urogenital Sinus (n).—The urogenital sinus extends from the caudal end of the vagina (m) to the external opening, which is situated ventrad of the anal opening. It is about a centimeter long and nearly as wide, and is marked off from the vagina by a circular fold of mucosa, while its inner surface presents longitudinal folds. On its ventral wall at its cranial end is the opening of the neck of the bladder, which is enclosed by a ring-like elevation of the mucosa, most prominent at the sides. The external entrance to the urogenital sinus forms the vulva.

The Clitoris.—The clitoris is a minute organ homologous with the penis and lying on the ventral floor of the urogenital sinus. Its distal end lies at the entrance of the urogenital sinus on its ventral border. In adult specimens the prepuce of the clitoris appears as a slight elevation of the integument surrounding a central vascular structure which appears red in the fresh organ. From the clitoris there are two small corpora cavernosa clitoridis (o) passing craniad and then diverging to be attached to the ischiatic rami. The ischiatic portion of each is covered by a muscle (ischiocavernosus). The clitoris is said to contain a bone.

Mammary Glands.—The mammary glands secrete the milk, and lie on the ventral surface of the body beneath the integument. The separate glands are closely gathered into two chief masses, one on each side the ventral middle line. Each of these extends from about the region of the fourth rib to the caudal end of the abdomen, ending over the pubic symphysis. On each side the glands are gathered into five groups, each of which is furnished with a nipple. The nipple is a projection of the integument, having near its distal end numerous fine openings for the ducts of the glands. The first two nipples are on the thorax, the other three on the abdomen, the most caudal ones being about two or three centimeters in front of the cranial edge of the pubis.

Rudimentary mammary glands and nipples are present in the male.

Muscles of the Urogenital Organs, Rectum, and Anus

([Figs. 113] and [114]).—The muscles connected with the caudal openings of the alimentary canal and of the urogenital organs are closely interrelated, a single muscle sometimes acting on parts of both systems. For this reason all these muscles are described together.

The region lying between the anus and the external opening of the urogenital organs is known as the perineum. The perineum is formed chiefly by muscles and fascia.

a. Muscles common to the Male and Female.

—M. sphincter ani externus ([Fig. 113], i; [Fig. 114], a).—This muscle is confounded with the levator scroti ([Fig. 113], j) or the levator vulvæ ([Fig. 114], b). The two take origin in common from the integument on the dorsum of the root of the tail dorsad of the fifth caudal vertebra. There the fibres from the opposite sides are intermingled. The common muscle passes ventrad about the tail as a flat band close to the integument. Dorsad of the anus the inner fibres of the muscles of the opposite sides are united. They then separate and surround the anus as a band five millimeters wide situated beneath the integument. Ventrad of the anus the fibres are again intermingled. Some fibres on each side then continue to the scrotum as the levator scroti ([Fig. 113], j) or to the vulva as the levator vulvæ ([Fig. 114], b). Fibres also pass onto the anal pouch and unite with the sphincter ani internus, forming the constrictors of the anal pouch (Strauss-Durckheim).

M. sphincter ani internus ([Fig. 113], h; [Fig. 114], c).—The sphincter ani internus is a broad and thick band of striated muscle-fibres which surrounds the rectum at the anus. Dorsad the band is about two centimeters broad, while ventrad it is less than one. In the ventral median line some of the fibres pass craniad to help in forming the bulbocavernosus muscle. The muscle surrounds the anal sac.

(The muscle here described under this name is that described under the same name in the cat by Strauss-Durckheim and Mivart; it corresponds, however, to a part of the sphincter ani externus of the dog, as described by Ellenberger and Baum.)

M. levator ani (or pubiocaudalis) ([Fig. 162], 11).—This muscle lies in the pelvic cavity. Each muscle forms a nearly vertical sheet, and between the two are the rectum and the urethra.

Origin from the symphysis of the pelvis.

Insertion into the midventral line of the centra of the third, fourth, and fifth caudal vertebræ, close to the muscle of the opposite side. This muscle is frequently continuous with the iliocaudalis ([Fig. 162], 11′).

Action.—Bends the tail and compresses the rectum.

M. ischiocavernosus ([Fig. 113], m; [Fig. 114], e).—A small, flat, spindle-shaped muscle which lies upon the crus of the penis or clitoris. Each has

Origin from the caudal border of the ramus of the ischium, about one centimeter from the median line.

Insertion, in the male, into the whole outer surface of the crus penis, or bulb of the corpus cavernosum penis. In the female the muscle is smaller than in the male, and the insertion is into the ventral surface of the urogenital sinus, at the base of the clitoris.

M. transversus perinei ([Fig. 114], i).—A small bundle of fibres which arises from the medial surface of the ischium, just dorsad of the origin of the ischiocavernosus, and passes mediad to join the sphincter ani internus (c).

M. caudoanalis (S.-D.) ([Fig. 113], f; [Fig. 114], g).—A slender, flat bundle of fibres having origin on the middle line of the ventral surface of the second and third caudal vertebræ. It passes caudoventrad, lying between the levator ani and the caudorectal ([Fig. 113], e; [Fig. 114], j), and unites with the ventral portion of the sphincter ani internus ([Fig. 113], h).

Action.—Draws the anus craniodorsad.

[Fig. 113].—Muscles of the Anus, Urogenital Organs, and Tail in the Male (Slightly Schematic).

One side of the pelvis has been removed, a, a′, M. extensor caudæ lateralis; b, M. abductor caudæ externus; c, c′, M. flexor caudæ longus; d, M. flexor caudæ brevis; e, M. caudorectalis; f, M. caudoanalis; g, M. caudocavernosus; h, M. sphincter ani internus; i, M. sphincter ani externus; j, M. levator scroti; k, M. rectocavernosus; l, M. bulbocavernosus; m, M. ischiocavernosus (cut); n, M. compressor urethræ membranaceæ. 1, tail; 2, rectum; 3, bulbourethral or Cowper’s gland; 4, prostate gland; 5, symphysis pubis; 6, penis; 7, glans penis; 8, testis; 9, spermatic cord.

M. caudorectalis ([Fig. 113], e; [Fig. 114], j).

Origin from the ventral surface of the sixth and seventh caudal vertebræ. A small, at first unpaired band two or three millimeters wide is formed, which passes cranioventrad, soon dividing into two lateral halves. These spread out over the sides of the rectum, forming a broad sheet of fibres which pass into the walls of the rectum, among the transverse fibres of the latter. This muscle is covered by the caudoanalis ([Fig. 113], f), caudocavernosus (g) (or caudovaginalis, [Fig. 114], h), iliocaudalis, and levator ani.

b. Muscles Peculiar to the Male

([Fig. 113]).—M. levator scroti (j).—This is a band of fibres which passes ventrad in the median line from the sphincter ani externus (i) onto the scrotum. Here it spreads out beneath the skin, forming especially a well-marked bundle in the median furrow between the two testes.

M. rectocavernosus, or retractor penis (k).—A small bundle of fibres which arises in two parts from the ventral surface of the sphincter ani internus (h). The two parts unite into a single bundle which passes caudad on the middle line of the ventral surface of the penis; it is inserted into the corpus cavernosum just proximad of the glans. The muscle is covered only by integument, and overlies the ischiocavernosus (m).

M. caudocavernosus (S.-D.) (g).—A slender bundle just craniad of the caudoanalis (f).

Origin on the median ventral line of the first two caudal vertebræ. The muscle passes caudoventrad, lying between the levator ani and the caudorectal (e). It divides into two bands, one of which is inserted into the base of the corpus cavernosum, while the other extends farther caudad and is inserted at the distal extremity of the corpus cavernosum.

Action.—Flexes the penis (bends it backward).

M. bulbocavernosus (accelerator urinæ) (l).—The two muscles cover the ventral surface of the penis.

Origin of each from a median raphe, which passes from the bulbous portion of the urethra toward the anus. The fibres pass toward the distal end of the penis and have their

Insertion into the distal half of the lateral surface of the corpus cavernosum penis.

M. compressor urethræ membranaceæ (n).—A thick layer of striated muscle-fibres which surrounds the urethra between Cowper’s gland (3) and the prostate (4). The fibres have a circular course, and the cranial ones are attached to the crura of the penis. The other fibres have no fixed attachment.

c. Muscles Peculiar to the Female

([Fig. 114]).—M. levator vulvæ (Strauss-Durckheim), or constrictor cunni (b).—This is homologous with the levator scroti of the male. It consists of a band of fibres which pass ventrad from the external sphincter ani (a) and surround the vulva (3), lying immediately beneath the integument.

M. constrictor vestibuli, or rectovaginalis (Strauss-Durckheim) (d).

[Fig. 114].—Muscles of the Anus and Urogenital Organs in the Female.

a, M. sphincter ani externus; b, M. levator vulvæ; c, M. sphincter ani internus; d, M. constrictor vestibuli; e, M. ischiocavernosus (cut); f, M. urethralis; g, M. caudoanalis; h, M. caudovaginalis; i, M. transversus perinei; j, M. caudorectalis. 1, the tail; 2, anus; 3, vulva; 4, rectum; 5, vagina; 6, neck of the bladder.

Origin from the sides of the sphincter ani internus (c). The muscle forms a distinct bundle two or three millimeters wide, which passes ventrocaudad and is inserted into the ventral surface of the urogenital sinus, caudad of the insertion of the ischiocavernosus (e).

M. caudovaginalis (Strauss-Durckheim) (h).—A slender band just craniad of the caudoanalis (g), and corresponding to the caudocavernosus of the male.

Origin from the median line of the ventral surface of the first two caudal vertebræ. The muscle passes caudoventrad, lying between the levator ani and the caudorectal (j), and is inserted into the ventral side of the urogenital sinus, at the base of the clitoris.

M. urethralis (f).—This consists of fibres surrounding the cranial part of the urogenital sinus and the caudal parts of the vagina and neck of the bladder.

Origin partly on the caudal part of the symphysis of the ischium, partly from the ventral surface of the urogenital sinus, where the fibres are attached to the corpora cavernosa clitoridis. The fibres pass dorsad over the surface of the sinus, and over the surface of the union of the vagina and neck of the bladder, to be inserted into the sides of the vagina and the dorsal surface of the urogenital sinus.

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