G.KOSS STEUCTUEE OF STEIATBD MUSCLE 269 



Others divide at one end into two tendons, and are called 

 biceps or two-headed muscles on that account. Still others 

 divide into three parts and are called triceps muscles. In 

 another form of muscle there are two bellies attached by 

 tendons and with tendons at each end. Such a form is 

 called a digastric muscle (see Fig. 115, B); while others 

 show as many as four bellied portions, and are called poly- 

 gastric muscles. 



Not all muscles end in tendons. In some cases the 

 muscle ends are attached directly to the bones. Nearly all 

 the muscles of the arms, legs, hands, and feet are of the 

 beUied variety. 



Flat muscles. On the trunk are found many muscles 

 which are flat and attached directly to the bones. Such 

 muscles are called flat muscles. They are of nearly uni- 

 form thickness throughout, and are found in places where 

 the belly would interfere with the action of other organs 

 or make the part too bulky. The muscles on the chest 

 are of this variety. 



Arrangement of striated muscles. — The bellied muscles 

 of the body are usually arranged in pairs (see Fig. 115, A). 

 Those which bend bones about a joint as pivot when they 

 contract are called flexors. The biceps muscle is a type 

 of a' flexor muscle. Those, on the contrary, which by con- 

 traction, extend a bone about a joint as pivot, are caUed 

 extensors. The triceps muscle, whose insertion is the end 

 of the ulna and whose origin is the humerus and scapula, 

 is an example of this type. The flexing and extending of 

 the forearm is due to the alternate contraction and relaxa- 

 tions of these two muscles and illustrates the typical paired 

 arrangement. 



Gross structure of striated muscle. — (See Ex. LIV.). 



