Part 161

THE VULVA

The =vulva= or =urogenital sinus= is the terminal part of the genital tract. It is continuous in front with the vagina, and opens externally at the vulvar cleft below the anus. There is no external line of demarcation between the vagina and vulva. The tube is about five inches (ca. 12 cm.) in length, measured from the external urethral orifice to the inferior commissure; dorsally it is considerably shorter. It is related dorsally to the rectum and anus, ventrally to the pelvic floor, and laterally to the sacro-sciatic ligament, the semimembranosus muscle, and the internal pudic artery. The external orifice or =vulvar cleft= (Rima vulvæ) has the form of a vertical slit, about four to six inches (ca. 10 to 15 cm.) high, and is margined by two prominent rounded folds, the labia. The =labia= of the vulva (Labia vulvæ) meet above at an acute angle, forming the =superior commissure= (Commissura dorsalis), which is about two inches (ca. 5 cm.) below the anus. Below they unite to form the thick rounded =inferior commissure= (Commissura ventralis), which lies about two inches (ca. 5 cm.) behind and below the ischial arch. When the labia are drawn apart, a rounded body, about an inch (ca. 2.5 cm.) wide, is seen in the inferior commissure; this is the =glans clitoridis=, the homologue of the glans penis. Overlying it is a thin fold, the =prepuce= of the clitoris (Præputium clitoridis). At the anterior extremity of the ventral wall of the vulva, i. e., about four or five inches (ca. 10 to 12 cm.) from the inferior commissure, is the =external urethral orifice= or meatus urinarius (Orificium urethræ externum). It readily admits the finger and is very dilatable. It is covered by a fold of mucous membrane, the free edge of which is directed backward.

=Structure.=—The =labia= are covered by thin, pigmented, smooth skin, which is richly supplied with sebaceous and sweat glands. This is continuous at a distance of about half an inch (ca. 1 to 1.5 cm.) from the free edge with a thin glandless mucous membrane. Between these is a layer of striped muscle, the =constrictor vulvæ=; this fuses above with the sphincter ani, and embraces the clitoris below, spreading out laterally at the inferior commissure. It constricts the vulvar orifice and elevates the clitoris. The =constrictor vestibuli= muscle embraces the vulva in front of the preceding; it is joined on either side by a band of unstriped muscle which arises from the first and second coccygeal vertebræ, and is homologous with the proximal part of the retractor penis. It constricts the vulva. Under this muscle in the lateral wall is a flattened, oval body, the =bulbus vestibuli= (Fig. 453); this is an erectile structure, homologous with the corpus spongiosum urethræ of the male. It is about two and a half to three inches (ca. 6 to 8 cm.) long, and an inch or more (ca. 3 cm.) wide. It consists of a venous network inclosed in a fibrous capsule, and is supplied with blood by a large branch of the internal pudic artery. The =mucous membrane= of the vulva is reddish in color, and forms longitudinal and transverse folds. It presents ventrally two linear series of small papillæ which converge toward the inferior commissure; these mark the orifices of the ducts of the =glandulæ vestibulares minores=. On either side of the dorsal wall is a group of eight to ten larger prominences on which the ducts of the =glandulæ vestibulares majores= (of Bartholin) open.

Quite exceptionally there may be found on either side of the urethral orifice the opening of the canals of Gartner (Ductus epoöphori longitudinales).

The =clitoris= is the homologue of the penis. It arises from the ischial arch by two crura, which unite to form a =body= as large as one’s little finger. This projects backward into the inferior commissure of the vulva, capped by a small rounded =glans=. The organ is composed of erectile tissue similar to the corpus cavernosum penis. The =ischio-cavernosus= (or erector clitoridis) is a very feeble muscle which depresses the clitoris. The veins of the clitoris communicate by an intermediate plexus on either side with the bulbus vestibuli.

THE FEMALE URETHRA

The female =urethra= (Urethra feminina) represents only that part of the canal of the male which lies between the internal urethral orifice and the openings of the ejaculatory ducts. Its length is about two inches (5 cm.), and its lumen is sufficient to admit of the introduction of the finger; it is, however, capable of remarkable dilatation if sufficient care and patience are exercised in the process. It lies centrally on the pelvic floor, and is related and attached dorsally to the vagina.

=Structure.=—The intrinsic =muscular coat= consists of longitudinal and circular layers of unstriped fibers. Between these is a layer of areolar tissue which contains a rich =venous plexus=. The =mucous membrane= is thrown into longitudinal folds when the canal is closed; it is highly elastic, and is covered with stratified epithelium.

The =urethral muscle= (M. compressor urethræ) embraces the urethra and is continued backward for some distance under the constrictor vestibuli. It is covered by a fibro-elastic membrane.

THE MAMMARY GLANDS

The =mammary glands= (Glandulæ lactiferæ) are modified cutaneous glands which are so closely associated functionally with the genital organs as to be considered accessory to them.

In the mare they are two in number, and are placed on either side of the median plane in the inguinal region. Each gland has the form of a short cone, much compressed transversely, and having a flat inner surface. It consists of the glandular mass or body of the gland (Corpus mammæ) and the =teat= or =nipple= (Papilla mammæ). The base is related to the abdominal wall, to which it is attached by areolar tissue, which contains a venous plexus, the superficial inguinal lymph glands, and a variable amount of fat. The apex is constituted by the teat, which is also flattened transversely and varies in length from one to two inches (ca. 2.5 to 5 cm.). Between the bases of the teats is the intermammary groove. On the apex of each teat two or three small orifices are placed close together; these are the openings of the lactiferous ducts.

=Structure.=—The =skin= over the glands is thin, pigmented, chiefly hairless, and supplied with numerous large sebaceous and sweat glands. Under this are two layers of =fascia= except on the teats. The superficial fascia presents no special features. The deep fascia consists of two laminæ detached from the abdominal tunic which descend on either side of the median plane, forming a =septum= between the two glands, and constituting their ligamentum suspensorium.

These laminæ are separated by a layer of areolar tissue, so that it is possible to remove one gland if diseased by careful dissection between the layers of the septum.

The =gland substance= or =parenchyma= is pinkish gray in color, and of firmer consistence than the fat which is found around and within the gland. It is inclosed by a fibro-elastic capsule which sends inward numerous trabeculæ; these form the =interstitial tissue=, and divide the gland into =lobes= and =lobules=. In the latter are the secretory =tubules= and =alveoli=, which unite to form the larger =ducts=. Each lobe has a duct, which opens at the base of the teat into a space called the =lactiferous sinus= (Sinus lactiferus); this is lined with mucous membrane, and from it two (or three) =lactiferous ducts= (Ductus lactiferi) pass through the extremity of the nipple. These ducts are lined with a non-glandular mucous membrane, which is covered with stratified squamous epithelium. They are surrounded by unstriped muscular tissue, the bulk of the fibers being arranged in a circular manner to form a =sphincter=.

The size and form of the mammary glands are subject to much variation. In the young subject, before pregnancy, they are small and contain little gland tissue. During the latter part of gestation, and especially during lactation, they increase greatly in size, and the gland tissue is highly developed. After lactation the secretory structures undergo marked involution, and the gland is much reduced in size. The relative amounts of gland substance and interstitial tissue vary greatly; in some cases a gland of considerable size contains little secretory tissue and is consequently functionally deficient.

=Vessels and Nerves.=—The =arteries= are derived from the =external pudic artery=, which enters the gland at the posterior part of its base. The =veins= form a plexus on either side of the base of the gland, which is drained by the =external pudic vein= chiefly. The =lymphatics= are numerous and pass chiefly to the superficial inguinal (or supramammary) lymph glands. The =nerves= are derived from the =inguinal nerves= and the =posterior mesenteric plexus= of the sympathetic system.

GENITAL ORGANS OF THE COW

The =ovaries= of the cow are much smaller than those of the mare, measuring usually about one to one and a half inches (ca. 3 to 4 cm.) in length, and a little less than an inch (ca. 2 cm.) in thickness in their largest part. They are oval in form, pointed at the uterine end, and have no ovulation fossa. They are situated usually a little above the middle of the lateral margin of the pelvic inlet in the non-pregnant subject, but may be found a little further forward. They are thus about 16 to 18 inches (ca. 40 to 45 cm.) from the vulva in a cow of medium size. The greater part of the surface of the gland is covered with germinal epithelium, the peritoneal epithelium being limited to a narrow zone along the attached border. Follicles of various sizes are often seen projecting from the surface, as well as corpora lutea; a corpus luteum verum has a pronounced yellow color, and may reach a width of half an inch or more (ca. 1 to 1.5 cm.).

FIG. 411.—OVARY OF COW.

1, Broad ligament of uterus; 2, ligament of ovary; 3, fimbria ovarica; 4, attachment of broad ligament; 5, surface of ovary covered with germinal epithelium; 6, corpora lutea; 7, Graafian follicle. (From Leisering’s Atlas.) ]

FIG. 412.—UTERUS OF COW, CONTRACTED, DORSAL VIEW.

a, Body of uterus; b, b′, horn of uterus; c, ovary; d, d′, triangular folds connecting horns of uterus (Lig. intercornualia). (After Zieger.) ]

The =Fallopian= or =uterine tubes= are long and less flexuous than in the mare. The junction with the cornu of the uterus is not so abrupt as in the mare, since the extremities of the horns are pointed. The uterine orifice of the tube is rather large and funnel-shaped. The fimbriæ are not so extensive as in the mare.

The =uterus= lies almost entirely within the abdominal cavity in the adult. The =body= is only about one inch (ca. 2 to 3 cm.) in length, although externally it appears to be much longer. This false impression is due to the fact that the posterior parts of the cornua are united by connective and muscular tissue and have a common peritoneal covering. The =cornua= are, therefore, really longer than they appear externally. They taper gradually toward the free end, so that the junction with the Fallopian tubes is not abrupt, as in the mare. The free part of the horn curves at first downward, forward, and outward, and then turns upward, forming a spiral coil. The =cervix= is about four or five inches (ca. 8 to 10 cm.) long; its wall is remarkably dense, and may be nearly an inch (ca. 2 cm.) in thickness. Its lumen, the =cervical canal=, is spiral, and is ordinarily tightly closed and very difficult to dilate. The =muscular coat= of the uterus is thicker than in the mare. It consists of an external longitudinal layer and two circular strata. The inner circular layer is about a fourth of an inch (ca. 6 mm.) thick in the cervix. The other layers are continued in the vagina. The =mucous membrane= of the horns and body presents as a characteristic feature the =uterine cotyledons= (Cotyledones uterinæ). These are oval prominences, about a hundred in number, which are either irregularly scattered over the surface or arranged in rows of about a dozen.

In the non-gravid uterus they average about ½ to ¾ inch (ca. 15 to 18 mm.) in length, ⅓ inch (ca. 8 mm.) in width, and ⅛ inch (ca. 2 to 4 mm.) in thickness. During pregnancy they become greatly enlarged and pedunculated. The larger ones then measure about 4 to 5 inches (10 to 12 cm.) in length, 1 to 1½ inches (3 to 4 cm.) in width, and 1 inch (2 to 2.5 cm.) in thickness. The deep face has a hilus at which the vessels enter. The rest of the surface has a spongy appearance, due to numerous crypts which receive the villi of the chorion.

The =uterine glands= are long and branched. The mucous membrane of the cervix is pale and forms numerous folds. The latter are arranged in several series which obliterate the lumen. At the external orifice (os uteri) the folds (Plicæ palmatæ) form rounded prominences arranged circularly, which project into the cavity of the vagina. There are no glands in the cervix, but a thick mucus is secreted by goblet cells.

FIG. 413.—UTERINE COTYLEDON OF COW.