130 



ELEMENTS OF PHYSIOLOGY 



220. Each muscle has another muscle or other muscles 

 that can undo the work done by it. Two muscles with oppo- 

 site action or function are said to be antagonists. There is a 

 great fan-shaped muscle called \hzpectoralis (n, Fig. 124) 



Cittnion of tht Hind 



FlG. 125. Full Figure Muscles (rear). 



on the chest, extending from the sternum to the arm. It 

 draws the arm downward and inward. This muscle is very 

 large in birds and is used in flying. To what muscle is it 

 an antagonist ? Muscles that bend joints are called flexors. 

 Those that straighten joints are called extensors. To which 

 kind does the biceps belong ? Which extensor muscle is its 

 antagonist? 



