The Collaborative International Dictionary of English v.0.48:
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. [1913 Webster]WordNet (r) 3.0 (2006):
metencephalon n 1: the part of the hindbrain that develops into the pons and the cerebellum