380 A YEAR IX SCIENCE 



shoulder blade. The muscle then passes over the front 

 of the humerus. Just below the elbow joint it is 

 attached by a tendon to the radius. When the biceps 



Tendon 



Fig. 176. The arm showing the attachments of the biceps 

 muscle. If the muscle contracts slightly the forearm will be lifted 

 over a great distance. 



contracts the distance between the forearm and the 

 shoulder is shortened. As a result, the forearm is bent 

 on the arm. If the biceps is decreased only a few 

 inches in length, the hand is moved through a much 

 greater distance. 



Situated on the back of the arm is the large triceps 

 muscle. By its contraction the forearm is straightened, 

 or extended. Where must its attachments be in order 

 to produce this action? 



Results of muscular action. The results of muscular 

 action are familiar to all of us. We know that motion, 

 heat, and energy are produced. To produce these, oxida- 

 tion is necessary, as a result of which both nerves and 

 muscles are being worn out and waste products are 



