sciatic nerve

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

• noun A sensory and motor nerve originating in the sacral plexus and running through the pelvis and upper leg.

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

• noun neuroanatomy A large nerve that starts in the lower back and runs through the buttock and down the lower limb.

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

• noun arises from the sacral plexus and passes about halfway down the thigh where it divides into the common peroneal and tibial nerves