\Gnath"ic\, a. [Gr. ? the jaw.] (Anat.)
Of or pertaining to the jaw.
{Gnathic index}, in a skull, the ratio of the distance from
   the middle of the nasofrontal suture to the basion (taken
   equal to 100), to the distance from the basion to the
   middle of the front edge of the upper jaw; -- called also
   {alveolar index}.
         Skulls with the gnathic index below 98 are
         orthognathous, from 98 to 103 mesognathous, and
         above 103 are prognathous.            --Flower.