opisthocoelian

from The Century Dictionary.

• Hollow or concave behind, as a vertebra: applied to vertebrœ whose bodies or centra are concave on the posterior face.
• Having opisthocœlian vertebræ, as a reptile; of or pertaining to the Opisthocœlia.
• noun A reptile with opisthocœlian vertebræ, or belonging to the order Opisthocœlia.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Anat.) Concave behind; -- applied especially to vertebræ in which the anterior end of the centrum is convex and the posterior concave.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective opisthocoelous