The Collaborative International Dictionary of English v.0.48:

Hyomental \Hy`o*men"tal\, a. [Hyo- + mental of the chin.]
   (Anat.)
   Between the hyoid bone and the lower jaw, pertaining to them;
   suprahyoid; submaxillary; as, the hyomental region of the
   front of the neck.
   [1913 Webster]