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. They are designed to 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 which separates Old World monkeys from New World monkeys.[1]
Otherwise the word callosity is generally reserved for describing the calluses found on the head of the three species of right whales.
