Circular Muscle

Just outside the submucosa is a band of circular muscle. The band surrounds the entire colon and is the first half of the muscularis externa. When this circular muscle contracts, it helps move waste material along the colon. If you prefer a more familiar example, envision a fat, flexible hose with some water standing in it. If you were to wrap your hand around that hose and squeeze, the water would move along. Circular muscle performs the same sort of function in the colon.