The Collaborative International Dictionary of English v.0.48:

Mesaticephalic \Mes`a*ti*ce*phal"ic\, a. [Gr. ? midmost + E.
   cephalic.] (Anat.)
   Having the ratio of the length to the breadth of the cranium
   a medium one; neither brachycephalic nor dolichocephalic.
   [1913 Webster]