The paired copulatory organs lying laterally in a cavity in the base of the tail in snakes and lizards (Peters 1964).
Paired sex organs of males, the bulge at the base of the tail
Penis of snake. Each snake has two penises, each of which is an independent fully functioning unit. Only one is used during mating. Each hemipene is sac-like and lies internally on either side of the base of the tail behind the vent in its own individual sheath. During mating the one that will be used is everted through an opening in the sheath and turned inside out. Hemipenes are covered by spines and hooks that help keep them in place during mating. A groove on the ventral boarder acts as a channel for sperm transfer.