An anatomical investigation on the muscles of the pelvic outlet in crab-eating monkey (Macaca irus) and Japanese monkey (Macaca fuscata) with special reference to their nerve supply.

For a fuller understanding of the nerve supply to the muscles of the pelvic outlet in man, 4 pelvic-halves of crab-eating monkeys and 6 pelvic-halves of Japanese monkeys were minutely dissected. 1) The composition of the pudendal plexus tends to be limited to 2 segments, S1 and S2. 2) If we consider the origin of the nerves, the pudendal plexus is divided into 2, the first or medial and the second or lateral parts. From the first part arise the pelvic splanchnic nerves, the nerve to the iliopubocaudalis and the nerve to the ischiocaudalis. From the second part the dorsal nerve of the penis or clitoris, the perineal nerve and the inferior rectal nerve originate. 3) A laminate arrangement exists among the 3 nerves from the first part at their origin; the pelvic splanchnic nerves are situated ventrally, and the nerve to the ischiocaudalis dorsally, with the nerve to the iliopubocaudalis in between. No obvious laminate arrangement exists among the 3 nerves from the second part. 4) The part of the iliopubocaudalis, contiguous with the rectal wall but without attaching to it, has no branches of supply from the perineal nerve and the inferior rectal nerve. 5) A detailed discussion of our findings in relation to man, is given below.