Forms the medulla oblongata in adults

• The posterior part of the hindbrain in developing vertebrates

Wiktionary Word definitions in Wiktionary
n. (context neuroanatomy English) The portion of the brain composed of the medulla oblongata.

WordNet Word definitions in WordNet
n. the posterior part of the hindbrain in developing vertebrates; forms the medulla oblongata in adults [also: myelencephala (pl)]

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Myelencephalon \My`e*len*ceph"a*lon\, n. [NL., from Gr. myelo`s marrow + E. encephalon.] (Anat.) The brain and spinal cord; the cerebro-spinal axis. Sometimes abbreviated to myelencephal . The metencephalon. --Huxley.

Wikipedia Word definitions in Wikipedia
The myelencephalon or afterbrain is the most posterior region of the embryonic hindbrain, from which the medulla oblongata develops.