Source : Webster's Revised Unabridged Dictionary (1913)

Microcephalic \Mi`cro*ce*phal"ic\, Microcephalous
\Mi`cro*ceph"a*lous\, a. [Micro- + cephalic, cephalous.] (Anat.)
   Having a small head; having the cranial cavity small; --
   opposed to {megacephalic}.

Source : WordNet®

microcephalic
     adj : having an abnormally small head and underdeveloped brain; "a
           nanocephalic dwarf" [syn: {microcephalous}, {nanocephalic}]