The Collaborative International Dictionary of English v.0.48:

Mesocoele \Mes`o*coe"le\, Mesocoelia \Mes`o*coe"li*a\, n. [NL.
   mesocoelia. See Meso-, and Coelia.] (Anat.)
   The cavity of the mesencephalon; the iter.
   [1913 Webster]