THE VAGINA, VESTIBULE, AND VULVA
(See also pp. 201-203.)
The vagina of the bitch is very long (ca. 12 cm) and extends horizontally through the pelvis before dipping beyond the ischial arch to join the vestibule (Figure 5-35/5,9).
Apart from the prominent dorsomedian fold that continues the cervix for a short distance, the interior of the undistended organ is obstructed by the irregular folds into which the wall naturally falls. These end at the junction with the vestibule (Figure 15-11 and Figure 15-12). The vestibule continues the downward slope of the vagina, which must be kept in mind when introducing a vaginal speculum or other instrument (Figure 5-2). This must be passed in a craniodorsal direction to clear the ischial arch before it can be advanced horizontally. During such examinations the dorsal fold combines with the lateral and ventral vaginal walls to simulate a cervix (pseudocervix).The cranial part of the vestibular floor (of the bitch) displays the tubercle and flanking depressions associated with the opening of the urethra, while the caudal part presents the fossa into which the glans of the clitoris projects (Figure 15-11/9,9') The functional significance of the urethral tubercle is not known. Darker patches of the lateral walls betray the positions of the vestibular bulbs, which are well-developed in the bitch but slighter and more diffuse (even insignificant) in the female cat. Vestibular glands are present only in the cat.
The thick labia of the vulva meet in a rounded dorsal and a pointed ventral commissure. More lateral folds that are sometimes apparent are believed to be homologous with the labia majora of human anatomy. The crura and body of the clitoris possess a little erectile tissue; the glans is largely of fatty fibrous tissue but sometimes contains a small bone, the os clitoridis. The queen has only a corpus cavernosum clitoridis and not a glans clitoridis.