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.