The rhythmic, wave-like contraction and relaxation of muscles so as to propagate motion, as of food in the digestive tract. More specifically, it is a type of intestinal motility, characterized by radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. With better reference to its etymology, peristalsis is progression of coordinated contraction of involuntary circular muscles (such that they "wrap around" its contents), which is preceded by a simultaneous contraction of the longitudinal muscle and relaxation of the circular muscle in the lining of the gut.