CHAPTER VIII. 



Tab. VIII. — BOPfEs of the arm. 



Fig. 1. a, the humerus ; the head, h, is a portion of a sphere, and 

 exhibits an example of the ball and socket^ or universal joint ; c, the 

 hinge joint, instanced in the elbow ; d, the radius ; e, the ulna. The 

 radius belongs more peculiarly to the wrist, being the bone which sup- 

 ports the hand, and which turns with it in all its revolving motions. 

 The ulna principally belongs to the elbow joint, for by it we perform 

 all the actions of bending or extending the arm. 



Fig. 2. a, the humerus : 6, shows the connexion of the radius, with 

 e, the ulna, at the elbow. The mode of articulation at the wrist is 

 »een, Fig. 1. 



