The female external genitalia include the mons pubis, labia majora, labia minora, clitoris, vestibule, bulbs of the vestibule and the greater vestibular glands. Collectively they form the vulva. All the formations and structures seen in the male are present in the female, but greatly modified for functional reasons. The essential difference is the failure in the female of the midline fusion of the genital folds. The scrotum is represented by the labia majora and the corpus spongiosum by the labia minora and the bulb of the vestibule, with corresponding vessels and nerves.
The mons pubis is the mound of hairy skin and subcutaneous fat in front of the pubic symphysis and pubic bones. It extends backwards on either side as the labia majora which are fatty cutaneous folds forming the boundary of the pudendal cleft. The round ligaments of the uterus end in the anterior part of each labium. A persistent processus vaginalis, and consequently an inguinal hernia, may reach a labium. The labia are joined in front as the anterior commissure; at the back they fade away behind the vagina, the connecting skin between them forming a low ridge, the posterior commissure, which overlies the perineal body.
The labia minora are cutaneous folds without fat lying internal to the labia majora and forming the boundaries of the vestibule. Their front ends split and unite to form the (dorsal) prepuce and (ventral) frenulum of the clitoris, while at the back they unite by a small skin fold, the frenulum of the labia.
The clitoris lies at the front ends of the labia minora. It is formed by two miniature corpora cavernosa and the anterior ends of the bulbs of the vestibule. Its free extremity, the glans, is highly sensitive to sexual stimulation and is usually overlapped by the prepuce.
The vestibule is bounded by the labia minora and contains the external urethral meatus, the vaginal orifice and the ducts of the greater vestibular glands.
The perineal membrane is wider but weaker than in the male, being pierced by the vagina. It gives attachment to the crura of the clitoris, each of which is covered by an ischiocavernosus muscle. Medial to each crus, attached to the perineal membrane at the side of the vagina, is a mass of erectile tissue, the bulb of the vestibule, one on each side of the orifices of the vagina and urethra. They join in front of the urethral orifice and pass forwards to the glans of the clitoris. Each bulb is covered by a bulbospongiosus muscle, whose fibres extend from the perineal body round the vagina and urethra to the clitoris. They form a perineal sphincter for the vagina in addition to its pelvic sphincter (the pubovaginalis parts of levator ani).
The greater vestibular glands (of Bartholin) form pea-shaped masses less than 1cm in diameter lying at the side of the vaginal opening, one behind the posterior end of each bulb and deep to bulbospongiosus. Each opens by a single duct 2cm long into the posterolateral part of the vaginal orifice, in the groove between the labium minus and the hymen or its remains. The duct may be subject to cyst formation, and the gland to infection (bartholinitis). The glands may play a minor role in lubricating the lower vagina. They are homologous with the bulbourethral (Cowper's) glands of the male, but unlike in the male they are superficial to the membrane.
The lesser vestibular glands are very small mucous glands with minute openings between the urethral and vaginal openings.
The hymen is a mucosal fold of variable extent and thickness at the margins of the vaginal opening. It may be absent or may even completely close the opening, in which case it must be incised at the age when menstruation begins. Its remains after rupture by the first sexual intercourse may form small tags (hymenal carunculae).
The deep perineal space is traversed by both the urethra and vagina. As in the male it contains the sphincter urethrae, deep transverse perineal muscles, nerves and vessels. The pudendal nerve and internal pudendal vessels have a corresponding course and distribution in the female deep perineal space and vulval region to that in the male deep and superficial perineal spaces, but the neurovascular branches are generally smaller. The pudendal nerve can be infiltrated with a local anaesthetic (pudendal nerve block) via a needle passed through the vaginal wall, directed towards the ischial spine and sacrospinous ligament which are palpable per vaginam.
Female orgasm
Sexual excitement induces vascular dilatation and engorgement in the vulva, especially the bulbs of the vestibule and glans clitoris, and is due, as in the male, to parasympathetic activity. There is dilatation of the thin-walled submucous veins of the vagina, which becomes moistened by a transudation of fluid through the mucous membrane. The vestibular glands probably make a negligible contribution. At the climax there is some vaginal smooth muscle and perineal skeletal muscle contraction, mediated by their sympathetic and somatic nerve supply respectively.