The Collaborative International Dictionary of English v.0.48:

Pterotic \Pte*ro"tic\, a. [Gr. ? wing + ?, ?, ear.] (Anat.)
   Of or pertaining to, or designating, a bone between the
   prootic and epiotic in the dorsal and outer part of the
   periotic capsule of many fishes. -- n. The pterotic bone.
   [1913 Webster]

   Note: The pterotic bone is so called because fancied in some
         cases to resemble in form a bird's wing
         [1913 Webster]