THE VAGINA
The vagina is about as long as the body of the uterus. It lies ventral to the rectum, dorsal to the bladder and urethra, and in lateral contact with the pelvic wall (Figures 22-8 and 22-13/5).
Although it is largely retroperitoneal, the extent of the covering depends on the degrees of filling of the bladder and rectum (see Figure 22-5). A small cranial part of the ventral aspect and a somewhat larger part of the dorsal aspect are always clad in peritoneum. This arrangement is useful because the dorsal part of the vaginal fornix provides a convenient approach to the peritoneal cavity for various procedures, including the recovery of ova.The vagina is thin walled, and although its lumen is normally closed by the dorsal and ventral walls falling together, the organ is remarkably distensible in length and circumference. The vaginal mucosa is ridged lengthwise, although the ridges are readily effaced on distention. The mucosa is normally pale pink but darkens when suffused with blood, as tends to happen on prolonged exposure to air during vaginoscopy. A transverse fold cranial to the opening of the urethra represents the remains of the hymen; although variable, it is generally more prominent than in other domestic species.