Urogenital diaphragm

Recommended video: Peritoneal relations [27:50]

Peritoneal cavity as seen in a parasagittal section.

The urogenital diaphragm, also known as the triangular ligament, is a strong sheet of striated skeletal muscle that occupies the area between the pubic symphysis and ischial tuberosities.

Both the urinary and genital orifices pierce through the urogenital diaphragm.

Several skeletal muscles make up the urogenital diaphragm including:

• the deep transverse perineal muscle arising from the ischium and inserting on the perineal body. It covers the space around the urogenital orifices.
• the external urethral sphincter arising from the pubis and ischium and inserting on the penis in males and the vagina in females. It surrounds the urethra.
• the bulbospongiosus muscle arising from the perineal body and enveloping the penis in males or the vagina in females before inserting on the penis or clitoris. It fills the medial space of the urogenital diaphragm.
• the ischiocavernosus muscles arising from the ischium and pubis and extending anteriorly and medially to the penis in males or the clitoris in females. They occupy the lateral edges of the urogenital diaphragm.
• the superficial transverse perineal muscle arising from the ischial tuberosity and inserting on the perineal body. It forms the base of the urogenital diaphragm.

A pair of thin membranes made of irregular connective tissue, the superior and inferior fascia, cover the muscles of the urogenital diaphragm.

The urogenital diaphragm functions to support the urethra. Contraction of the bulbospongiosus, deep transverse perineal and external urethral sphincter muscles assist in the propulsion of urine out of the urethra at the end of urination and, in males, semen during ejaculation. Additionally, the urogenital diaphragm provides support and protection to the surrounding organs.