lucidin

A callosity is another name for callus, a piece of skin that has become thickened as a result of repeated contact and friction.

When occurring on an animal's buttocks, as with baboons, they are specifically called ischial callosities. Ischial relates to the ischium: it forms the lower and back part of the hip bone.

The pads enable the monkeys to sleep sitting upright on thin branches, beyond reach of predators, without falling.

The ischial callosities are one of the most distinctive pelvic features ...