I III SKELETON 01 I ill i PP1 



external surface, is the much smaller and shall 



radius. I Opposite to th( upon the lower porl 



a broad deep depression, the olecranon }oi a Fig. n . which 



when the arm is extended. 



The humerus, like • 

 fn>m two or more epiph) I !)<• diaphyseal center ap] 



tilaginous al l>irth. During the I r appears in the up] 



the capitulum, t l r tubercle, the lesser tub A finally those for the ti 



epicondyle which appear between the tenth and twelfth yeai ' 



disappearanci ol th the epi| '1 the diaph ir until fi 



the twenty-se< ond yi 



Between lb the humi i 



epicondj . ar origin, the internal one giving 



the forearm, the external one to the superficial exti iVC the il 



the supracondyloid process. The ini 

 lower than does the external portion, and its surface rep: 

 by the thin bony plate between the coronoid and olecranon 1 I 



lv visible from behind. 



THE ULNA. 



The ulna Y\^. 117 to 119) is a three-sided prismatic long bone which is thick above and 

 quite small below. It is composed of a shaft and of a superior and an inferior extremity, 

 strong upper extremity presents a semilunar or greater sigmoid notch 

 which articulates with the trochlea of the humerus and is constricted in its middle. I 

 portion rests upon the upper surface of the coronoid pro Fig. ] 



jection directed anteriorly, and its posterior portion upon the 



strong bony j . the olecranon, which forms the tip of the elbow and : 



above the coronoid proc< ss. The external or radial side of th cimal extremil 



presents a notch, the radial or lesser sigmoid notch (Fig. 1 r the 1. 



passing downward from this cavity there is a rough longitudinal ridge, the 

 u;i. Immediately below the coronoid pi I a bn 1 whit: 



directed anteriorly, and is termed the tuberosity (Fig. 11 



Tlv 

 ridge gives origin to the greater portion of tl. 

 the tuberosity and th I the mu irm. 



The shaft of the bone becomes much thinner and more rounded toward its lower 

 so that while the hone resembles a three-sided prism in its upper cylindr 



iri its lower fourth. In the shaft may be recognized an anterior 1 :L and 



an internal or ulnar surface. The internal surface is separated from the posteri the 



dorsal border, and from the anterior one by the :'<».' The third border is sharp and 



is directed toward the radius; it separates the anterior from the poster: - called 



the interosseous ridge (Fig. 119 . The volar contains the nn: . which 



a nutrient canal passes toward the elbow within the bone, but otherwise the surface exhibits no 

 peculiarities. 



