5.3.5 Muscles of perineum
Before we look further at the penis we'll take a look at the muscles of the perineum that are on view in this dissection.
Both the bulb and the crura of the penis are surrounded by slender layers of muscle. The ischio-cavernosus muscles surround the crura, the bulbo-spongiousus muscle surrounds the bulb, and also the proximal corpus spongiosum. The bulbo-spongiousus muscle provides the propulsive force for ejaculation.
The most posterior fibers of bulbo-spongiosus pass backward to join a meeting point of muscles that's known as the perineal body. Joining the perineal body from behind are the most anterior fibers of the external anal sphincter.
Joining it from each side is an inconstant muscle, present here only on one side, the superficial transverse perineal muscle, which we'll remove. Just above the perineal body and the bulb of the penis is a thick triangular partition of fibrous and muscular tissue, the perineal membrane. We'll see it better in a minute.
Above the perineal membrane we're looking at the underside of the levator ani muscle complex, which is the main component of the pelvic diaphragm. The apparently empty space on each side is the ischio-rectal fossa, which is normally filled with fat.