perineum

The perineum is the region of the trunk between the pubic symphysis and the coccyx, extending from one sit bone (ischial) to the other and spanning the area between the thighs. In humans it forms the outlet of the pelvic cavity and supports the pelvic floor. The perineum is traditionally divided into two triangles: the anterior urogenital triangle and the posterior anal triangle, separated by a line between the ischial tuberosities and the perineal membrane. A midline fibromuscular structure called the perineal body serves as a central anchor for several pelvic floor muscles.

Boundaries and structures in the perineum include the perineal membrane, which spans from the inferior aspect of the pubic rami to the ischiopubic rami. The area contains external openings for the urinary and, in females, the vaginal tract, as well as the anal opening in the anal triangle. The perineum also houses glands that differ by sex: in males, the deep perineal pouch contains the bulbourethral glands; in females, portions of the superficial perineal pouch contain the greater vestibular (Bartholin) glands.

Muscles are organized into superficial and deep perineal pouches. The superficial pouch includes the bulbospongiosus, ischiocavernosus, and the superficial transverse perineal muscles. The deep pouch contains the external urethral sphincter (sphincter urethrae) and the deep transverse perineal muscles; the bulbourethral glands in males are located in this deep compartment, while in females the deep pouch has different components related to the urethra and vagina.

Innervation is primarily via the perineal branches of the pudendal nerve, with arterial supply from the internal pudendal system and venous drainage to the corresponding perineal veins. Functionally, the perineum supports pelvic organs, contributes to continence, and participates in sexual and reproductive activities. Clinically, it is involved in childbirth-related injuries, perineal tears, and episiotomy considerations.