174 



MOVEMENT 



of the arm is the same. Thus Figs. 114 and 115 both 

 represent a semiflexed arm, but in the first the 

 outstanding biceps shows that a movement of flexion 

 is in process of production, and in the second it is 

 the triceps (extensor muscle) which stands out most 



Fig. 114. — Flexion of an arm. 



Fig. 115. — Extension of an arm. 



markedly, while the biceps is flattened. The attitude 

 here represented corresponds to a phase in the extension 

 of the limb. 



In alternating movements, the antagonistic muscles 

 come into play. If extension of the arm is to be 



Fig. 116. — Alternating movr-men 

 and extension. 



Fig. 11' 



-Single movement of forcible exten- 

 sion (delivery of a blow). 



followed by flexion (Fig. 116), although the triceps 

 is the muscle directly concerned in the movement, 

 the biceps is also contracted, partly to arrest the 

 momentum of extension and partly so as to be ready 



