The Collaborative International Dictionary of English v.0.48:
Mesocephalic \Mes`o*ce*phal"ic\, a. [Meso- + cephalic.] (Anat.) (a) Of or pertaining to, or in the region of, the middle of the head; as, the mesocephalic flexure. (b) Having the cranial cavity of medium capacity; neither megacephalic nor microcephalic. (c) Having the ratio of the length to the breadth of the cranium a medium one; mesaticephalic. [1913 Webster]