While this term is used to refer to a layer of the pelvis that separates the deep perineal sac from the upper pelvis, such a discrete border of the sac probably does not exist.
While it has no official entry in Terminologia Anatomica, the term is still used occasionally to describe the muscular components of the deep perineal pouch. The urethra and the vagina, though part of the pouch, are usually said to be passing through the urogenital diaphragm, rather than part of the diaphragm itself.
Some researchers still assert that such a diaphragm exists, and the term is still used in the literature.
The term "urogenital diaphragm" is often confused with the pelvic floor, which is a true diaphragm supporting many of the pelvic organs.
In our school we operate with these terms:
The perineum actually is the pelvic exit, closed by the pelvic and urogenital diaphragms.
The pelvic diaphragm divides the minor pelvic cavity (true pelvis) into two compertments. They are the 1 Superior compartment, containing the pelvic viscera, and 2 The inferior compartment called ischiorectal fossa.
The urogenital diaphragm closes the anterior part of the ischiorectal fossa, leaving the fossa open posteriorly.
The urogenital diaphragm is made of 2(paired)muscles. the deep and superficial transverse perineal muscles. These two muscles join in front of the rectum, and form the perineal body.
Deep transverse perineal muscle: originates from the inferior pubic ramus snd the ramus of ischium. Runs medially and fuse in the midline. This muscle is interrupted once in male and twice in female, by the urethra and the vagina passing through it.
Around the urethra, the deep transverse perineal muscle forms a separate, ringlike valve, the sphincter urethrae in male, and a similar urethrovaginal sphincter in female.
This muscle does not attach to the symphysis. As a result, we can see a space between it, and the symphysis called as the retropubic space. Through this space exits the dorsal and deep arteries of penis/clitoris.
Superficial transverse perineal muscle: this muscle is a narrow bundle of skeletal muscle. Extend at the posterior border of the deep transverse perineal muscle, and insert on the perineal body.
The fascia of the urogenital diaphragm, the superficial and deep perineal fascia, lines both muscles. The superficial perineal fascia is lining the inferior surface of the urogenital diaphragm; meanwhile the deep fascia overlies the superior surface of the same diaphragm.