perineal muscle; in the male: origin, the perineal membrane fascia on the dorsum of the bulb of the penis; insertion, central tendon of the perineum and the median raphe on the free surface of the bulb; action, voluntarily constricts bulbous urethra when attempting to expel last drops after urination, or spasmodically with, and after, ejaculation to expel semen. In the female: origin, the dorsum of the clitoris, the corpus cavernosum, and the perineal membrane; insertion, central tendon of the perineum; action, acts as a weak sphincter of the vagina; when developed, is a part of “cross-member musculature” of pelvic floor that resists prolapse of pelvic viscera; surrounds and compresses greater vestibular gland, especially during erection of bulb of vestibule, expressing secretion. Nerve supply, pudendal (deep perineal branch).
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