CHAPTER XLVI 

 MUSCULAR SYSTEM 



Importance. The muscles .of our body constitute 

 about one-half of its weight. By means of these mus- 

 cles all the movements of the body and of its organs 

 are produced. Not only do they bring about the more 

 obvious motions of the legs and the arms, but also to their 

 action are due the contractions of the heart, of the 

 stomach, and of the other internal organs. 



Structure. In this study we will consider only the 

 larger muscles which are attached to the skeleton. 

 Muscles are of various shapes, but they are usually 

 larger in the middle than at either end. They are 

 attached at both ends to bones, usually by a tough, 

 white, inelastic cord, or tendon. 



If a complete muscle is examined, it will be found 

 to be covered with a thin sheet of connective tissue. 

 Y7hen this is removed, the muscles can readily be 

 divided longitudinally into bundles. These can be split 

 into smaller bundles, which in turn can be divided into 

 a number of long fibers. These fibers have the power 

 to contract and thus to become shorter and thicker. 

 When they shorten, they pull on the bone to which 

 they are fastened and move it. Their force is always 



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