A section through the S-1 spinal ganglion.
Observe:
1. The caudal edge of the anal fold lateral to the proctodeum.
2. The junction of the rectum and the anal part of the cloacal membrane.
Keywords: L-5 spinal ganglion, S-1 spinal nerve, S-1 ventral primary ramus, S-2 ventral primary ramus, S-3 ventral primary ramus, allantois, anal fold, buttock, cloacal membrane (anal part), digit 3, extravasated blood cells, hamstring muscle group, junction of rectum and cloacal membrane, labioscrotal swelling, median sacral artery, neural canal, proctodeum, sympathetic trunk, umbilical cord, vitelline (omphalomesenteric) artery, vitelline (omphalomesenteric) vein
Source: Atlas of Human Embryos.