The Collaborative International Dictionary of English v.0.48:

Basioccipital \Ba`si*oc*cip"i*tal\, a. [Basi- + occipital.]
   (Anat.)
   Of or pertaining to the bone in the base of the cranium,
   frequently forming a part of the occipital in the adult, but
   usually distinct in the young. -- n. The basioccipital bone.
   [1913 Webster]