Source : Webster's Revised Unabridged Dictionary (1913)

Metencephalon \Met`en*ceph"a*lon\, n. [Met- + encephalon.]
   (Anat.)
   The posterior part of the brain, including the medulla; the
   afterbrain. Sometimes abbreviated to meten.

Source : WordNet®

metencephalon
     n : the part of the hindbrain that develops into the pons and
         the cerebellum
     [also: {metencephala} (pl)]