Section 99. Unstriated Muscle Is Sometimes Called Involuntary, and

striated, voluntary muscle; but there is really not the connexion with the will that these terms suggest. We have just mentioned that the heart-muscle is striated, but who can alter the beating of the heart by force of will? And the striated muscles of the limbs perform, endless involuntary acts. It would seem that unstriated muscle contracts slowly, and we find it especially among the viscera; in the intestine for instance, where it controls that "peristaltic" movement which pushes the food forward. Voluntary muscle, on the other hand, has a sharp contraction. The muscle of the slow-moving snails, slugs, and mussels is unstriated; all the muscle of the active insects and crustacea (crabs, lobsters, and crayfish) is striated. Still if the student bears the exception of the heart in mind, and considers muscles as "voluntary" that his will can reach, the terms voluntary and involuntary will serve to give him an idea of the distribution of these two types of muscle in his own body, and in that of the rabbit.