The Collaborative International Dictionary of English v.0.48:

Prognathic \Prog*nath"ic\ (pr[o^]g*n[a^]th"[i^]k), a. (Anat.)
   Prognathous.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prognathic
    adj 1: having a projecting lower jaw [syn: prognathous,
           prognathic, hypognathous] [ant: opisthognathous]