Source : Webster's Revised Unabridged Dictionary (1913)

Macrencephalic \Mac`ren*ce*phal"ic\, Macrencephalous
\Mac`ren*ceph"a*lous\, a. [Macro + encephalic, encephalous.]
   Having a large brain.

Source : WordNet®

macrencephalous
     adj : having a large brain case [syn: {macrencephalic}]