Female External Genitalia Anatomy
The perineal membrane is thinner in the female than in the male and is pierced by both the vagina and the urethra. Attached to the inferior surface of the membrane is erectile tissue similar to that in the male, namely the crura of the clitoris and the bulbs of the vestibule covered by the thin ischiocavernosus and bulbospongiosus muscles, respectively (Figs 5.40 & 5.41). The right and left crura attach to the medial margins of the ischial and pubic rami. Passing forwards and medially they merge beneath the pubic symphysis to form the shaft of the clitoris. This turns downwards and backwards towards the urethral opening, and its tip is capped by the glans of the clitoris.
The paired bulbs of the vestibule surround the urethral and vaginal openings (Fig. 5.41). Anteriorly, they taper and fuse into a midline structure that terminates as the glans of the clitoris. The posterior end of each bulb is expanded and covers the greater vestibular (Bartholin’s) gland. This gland is approximately 1 cm in diameter and drains into a minute duct, which opens into the vestibule lateral to the vaginal opening. The gland may be the site of cyst formation (Bartholin’s cyst) or may become infected (Bartholin’s abscess) requiring surgical intervention. Superficial transverse perineal muscles pass laterally from the bulbs of the vestibule to the ischial tuberosities.
The most superficial parts of the female external genitalia are the skin folds, the labia majora (Fig. 5.40). These meet anteriorly at the mons pubis. The mons is a pad of fat overlying the pubic symphysis and covering most of the clitoris. Between the labia majora lie the two labia minora, which become more prominent anteriorly. The labia minora fuse in the midline, forming two folds of skin around the glans of the clitoris. The hood-like anterior fold comprises the prepuce of the clitoris and the smaller posterior fold forms the frenulum. Posteriorly, the labia minora are united by a delicate fold, the fourchette, which is usually torn during vaginal delivery.
The labia minora enclose a cleft, the vestibule, into which the vagina and urethra open (Fig. 5.41). The vaginal opening (introitus) is an anteroposterior slit, usually surrounded by a fringe of skin, the hymen. The external urethral meatus lies approximately 1 cm anterior to the vaginal opening.
The term vulva is used to describe the mons pubis, the labia majora and minora, the clitoris and vestibule.
Cutaneous innervation and blood supply
The mons pubis and the anterior parts of the labia are innervated by the ilioinguinal nerves (Fig. 4.24). The posterior part of the vulva receives cutaneous innervation from the labial branches of the pudendal nerves, supplemented by branches of the posterior cutaneous nerves of the thighs and the perineal branches of the fourth sacral nerves. Anaesthetic injected near the ischial spines will produce pudendal nerve block, which is sometimes used during childbirth.
The skin and subcutaneous tissues are supplied by the internal pudendal artery and the superficial and deep external pudendal branches of the femoral artery. Most of the venous blood passes into the venae comitantes of the internal pudendal artery, but anteriorly some blood drains by external pudendal veins into the great saphenous vein. Lymph from the skin and superficial tissues, including the vestibule and lower vagina, passes to the superficial inguinal nodes (Fig. 6.11), while lymphatics from deeper structures follow the course of the arteries to reach the internal iliac nodes.