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 direc- 

 tions. 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 invol- 

 untarily. 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 responsi- 

 bility and trouble of the activity of these organs ; other- 

 wise, 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, 



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