Urogenital Diaphragm

The outlet of the pelvis is spanned by two muscular sheets - a deeper "pelvic diaphragm" and a more superficial "urogenital diaphragm." The pelvic diaphragm forms the floor of the pelvic cavity, and the urogenital diaphragm fills the space within the pubic arch. The muscles of the male and female urogenital diaphragm include the following: (1) "superficial transversus perinei," a small bundle of muscle fibers that pass along the back border of the urogenital diaphragm and assists other muscles in supporting the pelvic tissues; (2) the "bulbospongiosus" muscles, which are united and surround the base of the penis; (3) the "ischiocavernosus muscle," a tendinous structure that extends down to the margin of the pubic arch and assists the function of #2; and (4) the "sphincter urethrae" are muscles that arch around the urethra and unite with those on the other side. Together they act as a sphincter that closes the urethra by compression and opens it by relaxation to control the flow of urine.