cheek pouch

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

• noun A pocketlike fold of skin in the cheeks of various animals, such as squirrels, gophers, and monkeys, that functions as a means of carrying food.

from The Century Dictionary.

• noun A special dilatation of the skin or of the skin and mucous membrane of the cheek, forming a pouch or bag outside the teeth, in many animals, as monkeys, squirrels, and various other rodents.

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

• noun anatomy, zoology A pouch in the cheek of some animals, usually used to carry food.

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

• noun a membranous pouch inside the mouth of many rodents (as a gopher)