Part 63

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.

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.