The Collaborative International Dictionary of English v.0.48:

Presphenoid \Pre*sphe"noid\, a. (Anat.)
   Situated in front of the sphenoid bone; of or pertaining to
   the anterior part of the sphenoid bone (i. e., the
   presphenoid bone).
   [1913 Webster]

   Presphenoid bone (Anat.), the anterior part of the body of
      the sphenoid bone in front of the basisphenoid. It is
      usually a separate bone in the young or fetus, but becomes
      a part of the sphenoid in the adult.
      [1913 Webster]