MUSCULAR SYSTEM 379 



the result of a contraction, and hence is due always 

 to a pull and never to a push. 



Tendons are useful because they permit the thick 

 contracting part of the muscle to be at some distance 

 from the part to be moved. This avoids bulkiness, espe- 

 cially at the joints. The muscles which move the 

 finger, for example, are located in the forearm. Ten- 

 dons, which can easily be traced on the back of the 

 hand, extend from these muscles to the finger bones. 

 It is evident that this arrangement makes the hand 

 smaller and more graceful and permits of greater 

 ease and delicacy in its movements. 



Blood and nerve supply. Muscles are well supplied 

 with blood. Fresh meat is always deep red in color 

 due to the presence of a great quantity of blood. 

 Nerves are also very numerous in muscles ; in fact, some 

 muscles are altogether under the control of the nervous 

 system, and are known as voluntary muscles. Most of 

 the muscles fastened to the bones are of this type. Other 

 muscles, such as those in the walls of the stomach, 

 in the walls of the blood vessels, or in the heart are 

 perhaps not completely under nerve control. At any 

 rate, we can not control them and they are called 

 involuntary muscles. 



Action of muscles. The action of a muscle can best 

 be understood by a consideration of the arm muscles. 

 The forearm is bent or flexed by the action of a large 

 muscle on the front of the arm, known as the biceps 

 muscle. This is attached by two tendons to the 



