Ischial callosity

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.In whales, the term callosity refers to the rough, calcified skin patches found on the heads of the three species of right whales. These callosities are a characteristic feature of the whale genus Eubalaena; because they are found on the head of the whale and appear white against the dark background of the whale's skin, they make it very easy to identify these species. The callosities themselves are grey; the white appearance is due to large colonies of whale lice, whale barnacles and parasitic worms which reside on them. Young whales and diseased individuals are often infested with a different species of cyamid, which gives an orange hue rather than white on these whales. Callosities arise naturally and are present even in late-term whale fetuses, although the work of lice digging into the surface of the skin may make them more jagged and hard over time.