Source : Webster's Revised Unabridged Dictionary (1913)

Myelencephala \My`e*len*ceph"a*la\, n. pl. [NL. See
   {Myelencephalon}.] (Zo["o]l.)
   Same as {Vertebrata}.

Source : WordNet®

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

myelencephala
     See {myelencephalon}