The urethra of the bitch (urethra feminina) () corresponds to the preprostatic part of the pelvic urethra in the male. It is approximately 0.5 cm in diameter and 7 to 10 cm long. It originates from the urinary bladder at or near the cranial edge of the symphysis pelvis. It extends caudodorsally to enter the genital tract caudal to the vaginovestibular junction on the urethral tubercle. Its dorsal wall is in close apposition to the ventral wall of the vagina. Structurally, the female urethra resembles that of the male. It is lined by folded mucous membrane, allowing the urethral lumen to expand considerably when under pressure. The mucosa is nonglandular, and the submucosa is highly vascular. Lymph nodules are also present. The musculature of the female urethra consists of outer and inner longitudinal and middle circular layers of unstriped muscle. The smooth muscles become less conspicuous near the entrance of the urethra into the vestibule. At the external urethral orifice, voluntary striated muscle (m. urethralis) encircles all but the dorsal surface of the urethra, which is in close contact with the vestibule. These circular fibers form a prominent sphincter at the external orifice.
Female Urethra: Vessels and Nerves
The external genitalia and urethra of the female are supplied with blood through the vaginal and the external and internal pudendal arteries. In the inguinal region the external puden-dal artery sends branches to the labia (cranial labial artery), corresponding to the scrotal branches in the male. The vaginal artery supplies the vulva by means of the cranial and caudal vestibular branches. The ventral perineal artery supplies branches to the labia dorsally. The clitoris is supplied by branches of the internal pudendal artery, corresponding to the dorsal and deep penile arteries. The vestibular bulb is also supplied by the internal pudendal artery (homologous to the artery of the bulb in the male).
The bilateral dorsal veins from the clitoris join each other at the ischial arch and then separate again (after a distance of 1 or 2 cm) into internal pudendal veins, which drain into the internal iliac veins. The vestibular bulb is drained by a separate tributary of the internal pudendal. Valves are apparent in most of the veins, including the common trunk of the dorsal veins of the clitoris. The dorsal arteries and veins of the clitoris are not actually dorsal to the clitoris, in the manner of the comparable penile vessels. They curve ventrally around the ischial arch and run caudoventrally along the ventral surface of the clitoris that corresponds to the dorsum of the penis. Lymphatic drainage compares with that of the external genitalia of the male.
The sensory afferent nerves to the external genitalia are derived from the pudendal nerves (). According to these authors the genital branches of the genitofemoral nerve do not reach the external genitalia.
The glans clitoridis receives its sensory nerves from the pudendal (dorsal nerve of the clitoris). Motor impulses to the urethral muscle and to the vestibular and vulvar constrictors also pass through the pudendal nerve. Autonomic innervation to the external genitalia and urethra in the female is through the hypogastric and pelvic nerves. It includes principally sympathetic fibers that innervate the musculature of the blood vessels.