a muscle of the perineum, the area between the anus and the genitals. In the male, it surrounds the bulb (the enlarged inner end of the structure that surrounds the urethra) of the penis and can be contracted to expel the last drops of urine or semen. In the female it is divided into halves that extend from just behind the clitoris to the central tendon of the perineum and serves to constrict the vagina.