heart and the motion of the chest never cease. In fact, the power to
execute spontaneous movement is the most characteristic property of
living animals.

65. Kinds of Muscles. Most of the bodily movements, such as affect
the limbs and the body as a whole, are performed by muscles under our
control. These muscles make up the red flesh or lean parts, which,
together with the fat, clothe the bony framework, and give to it general
form and proportion. We call these muscular tissues voluntary
muscles, because they usually act under the control of the will.

The internal organs, as those of digestion, secretion, circulation, and
respiration, perform their functions by means of muscular activity of
another kind, that is, by that of muscles not under our control. This work
goes on quite independently of the will, and during sleep. We call the
instruments of this activity involuntary muscles. The voluntary
muscles, from peculiarities revealed by the microscope, are also known as
striped or striated muscles. The involuntary from their smooth, regular
appearance under the microscope are called the unstriped or non-striated
muscles.

The two kinds of muscles, then, are the red, voluntary, striated
muscles, and the smooth, involuntary, non-striated muscles.

66. Structure of Voluntary Muscles. The main substance which clothes
the bony framework of the body, and which forms about two-fifths of its
weight, is the voluntary muscular tissue. These muscles do not cover and
surround the bones in continuous sheets, but consist of separate bundles
of flesh, varying in size and length, many of which are capable of
independent movement.