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 CHAPTER IV

THE MUSCLES

It has already been stated that there are at least two muscles attached to a bone to move it in opposite directions. Since there are two hundred and six bones, you are not surprised to learn that to move the bones and accomplish the various purposes just stated, there are five hundred and twenty-six (526) skeletal muscles.

Two Kinds of Muscles.—All muscles are controlled by means of the nervous system. Some of them are directed by parts of the brain that work consciously; others are controlled by the spinal cord and the parts of the brain that work unconsciously. Those of the first kind are usually controlled by the will, but they sometimes act involuntarily. They are called voluntary muscles. They move the bones and are located in the limbs and near the surface of the trunk (Fig. 44). The other kind of muscles are never controlled by the will, and are called involuntary muscles. We cannot cause them to act, nor can we prevent them from acting. They contract more slowly than the voluntary muscles. Most of them are tubular and found in the cavity of the trunk. The involuntary muscles belong to the internal organs, and relieve the will of the responsibility and trouble of the activity of these organs; otherwise, the mind would have no time for voluntary actions.

Gross Structure of Voluntary Muscles.—A beefsteak is seen to be chiefly red, although parts of it are white or yellowish. The white or yellowish flesh is fat; the red,