brain stem

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The portion of the brain, consisting of the medulla oblongata, pons Varolii, and midbrain, that connects the spinal cord to the forebrain and cerebrum.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun anatomy The part of the brain that connects the spinal cord to the forebrain and cerebrum.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the part of the brain continuous with the spinal cord and comprising the medulla oblongata and pons and midbrain and parts of the hypothalamus