The Collaborative International Dictionary of English v.0.48:

Hypapophysis \Hy`pa*poph"y*sis\, n.; pl. Hypapophyles. [NL.
   See Hypo-, and Apophysis.] (Anat.)
   A process, or other element, of a vertebra developed from the
   ventral side of the centrum, as h[ae]mal spines, and chevron
   bones. -- Hy`pa*po*phys"i*al, a.
   [1913 Webster]