Ischial

Is″chi‐al (ĭs″kĭ‐al), a.(Anat.) Of or pertaining to the ischium or hip; ischiac; ischiadic; ischiatic.

Ischial callosity(Zoöl.), one of the patches of thickened, hairless, and often bright-colored skin, on the buttocks of many apes, as the drill.