Source : Webster's Revised Unabridged Dictionary (1913)

Opisthocoelian \O*pis`tho*c[oe]"li*an\, Opisthocoelous
\O*pis`tho*c[oe]"lous\, a. [Gr. ? behind + ? hollow,] (Anat.)
   Concave behind; -- applied especially to vertebr[ae] in which
   the anterior end of the centrum is convex and the posterior
   concave.