S24 



ELEMENTARY PHYSIOLOGY 



supination (Fig. 101, A) ; when the back, pronation 

 (Fig. 101, B). 



The forearm is composed of two bones ; one, the ulna, 

 which articulates with the humerus at the elbow by the 

 hinge-joint already described, in such a manner that it can 



Fig. 101. 



The bones of the right forearm in supination (A) and pronation (B). 

 H, humerus ; R, radius : U, ulna. 



move only in flexion and extension (see p. 320), and has no 

 power of rotation. Hence, when the elbow and wrist are 

 rested on a table, this bone remains unmoved. 



But the other bone of the forearm, the radius, has its 

 small upper end shaped like a very shallow cup with thick 



