Source : Webster's Revised Unabridged Dictionary (1913)

Ischial \Is"chi*al\, a. (Anat.)
   Of or pertaining to the ischium or hip; ischiac; ischiadic;
   ischiatic.

   {Ischial callosity} (Zo["o]l.), one of the patches of
      thickened hairless, and often bright-colored skin, on the
      buttocks of many apes, as the drill.