{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.