116 PRACTICAL ANATOMY. 



The posterior border is rounded and slightly twisted. It 

 begins at the olecranon process, and is subcutaneous in 

 the upper half of its extent. The anterior surface is 

 flat, slightly concave, and broad. The posterior surface 

 is slightly concave, and crossed by several lines. The 

 inner surface is rounded, and subcutaneous in the lower 

 part. These surfaces afford attachment to the muscles 

 in this region. 



The inferior extremity of the ulna is small, and pre- 

 sents an articular head and a styloid process. The 

 head is rounded, and articulates below with the triangu- 

 lar cartilage. It presents a lateral articular surface for 

 articulation with the inner surface of the lower extrem- 

 ity of the radius. The styloid process projects down- 

 ward from the inner surface. It is about one-fourth of 

 an inch long, blunt and strong, and serves for the attach- 

 ment of the interarticular fibre-cartilage. 



The ulna develops by three centres, one for the 

 olecranon, one for the shaft, and one for the inferior 

 extremity. A secondary centre is often found in the 

 coronoid process. 



THE RADIUS. 



]The radius is the outside bone of the forearm. It is 

 a long bone, and presents for examination an upper 

 extremity, a shaft, and a lower extremity. The upper 

 extremity prpspnt.s t.hp hpi^j- a flattened, concave, shal- 

 1nwny]jjndftr of hone T which articulates above with the 

 nflfipr nv radial jifiad of the humerus! The surlace is 

 slightly cup-shaped, about rive-eighths inch in diameter. 

 It is continuous with the lateral articular surface, which 

 is an articular ribband of cartilage, deficient only at the 

 outer fourth of the head of the bone. It articulates 

 with the lesser sigmoid cavity. Immediately below the 

 head is the neck, a marked constriction of the bone ; 



