mastoid process

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

• noun A conical protuberance of the posterior portion of the temporal bone that is situated behind the ear in humans and many other vertebrates and serves as a site of muscle attachment.

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

• noun The conical, nipple-like projection of the petrous part of the temporal bone, that is situated behind the ear in humans and many other vertebrates, and serves as a site of muscle attachment.

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

• noun process of the temporal bone behind the ear at the base of the skull