Source : Webster's Revised Unabridged Dictionary (1913)

Orthognathous \Or*thog"na*thous\, a. [Ortho- + Gr. ? the jaw.]
   (Anat.)
   Having the front of the head, or the skull, nearly
   perpendicular, not retreating backwards above the jaws; --
   opposed to {prognathous}. See {Gnathic index}, under
   {Gnathic}.