THE MUSCLES 



125 



muscles because the internal organs are called the viscera. 

 The quicker, stronger-acting voluntary mus- 

 cles are sometimes called the skeletal muscles 

 because nearly all of them are attached to 

 bones. Exceptions to this are the sphincter 

 muscles or circular muscles that surround 

 orifices, as the muscles that pucker the 

 mouth and squint the eye. There are about 

 five hundred voluntary muscles. By study- 

 ing the figures you will notice that the mid- 

 dle portion of these muscles is usually large 

 and full, and that the muscles taper to small 

 cords at the ends (Fig. 113, etc.). The 



FIG. 115. Striated v 



Muscular Fibers muscles of the calf move the foot, and the 

 (a) terminating musc i es o f t h e forearm move the hand. If 



in lendon (o). 



the full round muscles extended down over 

 the wrists and ankles, it would make these as large around 

 as the forearm or calf, 

 and the wrists and 

 ankles would be very 

 clumsy and awkward. 

 It is found that the con- 

 nective tissue which 

 binds the fibers of a mus- 

 cle into bundles and forms 

 sheaths for the bundles, 

 extends beyond the mus- 

 cular tissue and unites to 

 form a dense, inelastic, 



White 



a tendon 

 . \ .-i-,, rv 



115). The fibers are 

 very closely packed together and make a very strong cord. 

 One no thicker than a lead pencil is strong enough to 

 support twice the weight of the body. A tendon contains 



FlG. 116. Diagram to show the Action of the 

 Biceps Muscle of the Arm. 



COrd The two tendons by which the muscle is attached to 

 the scapula are seen at a ; P, the point of attach- 

 (Fig. ment of the muscle to the radius; F t the elbow 

 joint; W, the weight of the hand. 



