Life and Health 



FIG. 22. 

 Left Radius and Ulna. 



is often broken by falls, or by blows upon 

 the shoulder or arm. 



The humerus is the strongest 

 bone of the upper extremity. 

 Its rounded head rests on the 

 socket of the shoulder-blade, 

 forming a ball-and-socket joint, 

 which permits great freedom of 

 motion. 



When the shoulder is dislo- 

 cated or " put out of joint," the 

 head of the humerus is forced 

 out of its socket. The lower 

 end of the bone is grooved to 

 help form a hinge joint at the 

 elbow with the bones of the 

 forearm. 



52. The Forearm. The fore- 

 arm contains two long bones, 

 the ulna and the radius. 



The ulna, so called because 

 it forms the elbow, is the longer 

 and larger bone of the fore- 

 arm, and is on the same side 

 as the little finger. It is con- 

 nected with the humerus by a 

 hinge joint at the elbow. It 

 is prevented from moving too 

 far back by a hook-like pro- 

 jection called the olecranon 

 process, which makes the 

 sharp point of the elbow. 

 The radius is the shorter of 



