Source : Webster's Revised Unabridged Dictionary (1913)

Myelencephalon \My`e*len*ceph"a*lon\, n. [NL., from Gr. ? marrow
   + E. encephalon.] (Anat.)
   (a) The brain and spinal cord; the cerebro-spinal axis; the
       neuron. Sometimes abbreviated to myelencephal.
   (b) The metencephalon. --Huxley.

Source : WordNet®

myelencephalon
     n : the posterior part of the hindbrain in developing
         vertebrates; forms the medulla oblongata in adults
     [also: {myelencephala} (pl)]