THE VESTIBULE AND VULVA
The vestibule slopes ventrally to open between the labia (see Figure 29-11). It is less distensible than the vagina and its side walls are normally in contact. When drawn apart, the opening of the urethra is exposed at the cranial end of the vestibule and, at the other, the fossa containing the glans of the clitoris (see Figure 29-14).
A large depression caudolateral to the urethral opening marks the location of the major vestibular gland, about 3 cm long, which is enclosed within the urogenital diaphragm. The vestibular mucosa is generally darkened over the gland.The rounded, rather low labia are often marked by trauma sustained at previous calvings. Simple inspection exposes relatively little of the slender clitoris because the glans is fused with the prepuce. The vulva of the freemartin, abnormally small, is surrounded by unusually long hair.
The vestibule penetrates the urogenital diaphragm (perineal membrane), which fills the gap between the rectovaginal septum and the pelvic floor. The fascia of the diaphragm arises from the pelvic floor, bends around and attaches to the wall of the vestibule, and merges with the rectovaginal septum, the lower edge of the pelvic diaphragm, and the parietal pelvic fascia. One importance of the arrangement lies in its anchorage of the genital tract, opposing the drag of the gravid uterus as it sinks into the abdomen and the backward drag during calving.
Figure 29-14 The bovine reproductive organs, dorsal view. A, The vagina and the vestibule have been opened in the specimen. B, The greater part of the tract is shown opened in the schema. 1, Ovary; 2, uterine tube; 2', infundibulum; 3, uterine horn; 4, intercornual ligament; 5, wall of uterus dividing the two horns; 6, body of uterus with caruncles; 7, broad ligament; 8, cervix; 9, vaginal part of cervix; 10, fornix; 11, vagina; 12, position of former hymen; 13, external urethral orifice and suburethral diverticulum; 14, major vestibular gland and its excretory orifice; 15, vestibule; 16, glans of the clitoris; 17, right labium.
Constrictor vestibularis and constrictor vulvae muscles are associated with the vestibule and vulva. The former, the more important, incorporates some fascicules that continue from the levator ani and form the perineal body. It runs over the wall of the vestibule caudal to the diaphragm and passes below the vestibule to join its fellow; on contraction it narrows the genital passage and raises a ridge in its floor. The constrictor vulvae, through its insertion to the vulva and adjacent skin, may cause the opening to gape.