CHAPTER XXV. 

 THE MUSCLES. 



The Number of Muscles. There are over five hun- 

 dred muscles in the human body. These vary in size from 

 less than an inch in length, in the ear and in the larynx, 

 to a foot and a half long in the thigh. 



The Arrangement of Muscles. The muscles of the 

 two sides of the body are paired, and normally are about 

 equal in size and strength. The muscles of the limbs are 

 further paired into flexors, which bend, and the extensors, 

 which straighten the limbs. The muscles are also arranged 

 more or less in layers. There is generally a superficial 

 layer and a more deep-seated layer. 



Forms of Muscles. Muscles are of various shapes. 

 The prevailing form in the limbs is spindle-shaped, or fusi- 

 form. This is convenient, as the thicker middle portion 

 of the muscle is opposite the more slender part of the 

 bone, while the tendons at the ends of the muscles are 

 opposite the enlarged ends of the bones at the joints. 

 Some muscles are flat, some have their fibers arranged 

 like the barbs of a feather, and are hence called penni- 

 form. Some muscles have a tendon in the middle which 

 runs through a loop, as in the case of the muscle which 

 depresses the lower jaw. As already stated, muscles 

 which close openings are circular, and are called sphincter 

 muscles. 



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