Erector Penis (a, fig. 227). - These are two short, thick fleshy muscles which arise from the crest of the ischium, and are inserted into the cruras of the penis.

They assist in bringing about erection, by preventing the free outflow of blood from the corpora cavernosa and causing an engorgement of its cells and vessels.

Retractor Penis (c, fig. 227). - This consists of two bands of pale unstriped muscle, which arise from the under surface of the coccygeal or tail bones, and after winding round the rectum converge together below the anal opening, and are continued forward beneath the corpus spongiosum to the extremity of the penis.

Contracting, they draw the penis back into the sheath after erection.