THE RADIUS. 



287 



rarity. Even in cases of separation of the lower epiphysis of the radius, or of 

 Colles's fracture, the strain reaches the tip of the ulnar styloid through the internal 

 lateral ligament and produces fracture of that process, or of the ulnar diaphysis at 

 its smallest point (about three-quarters of an inch above the lower end), rather than 

 separation of the epiphysis. 



As the growth of the ulna depends almost exclusively upon the lower epiphy- 

 sis, injuries stopping short of recognizable disjunction have been followed in a 

 number of cases by failure of development, resulting in lateral displacement (adduc- 

 tion ) of the hand. 



Landmarks. — The olecranon can always easily be felt at the back of the 

 elbow. It is somewhat nearer the internal than the external condyle. With the 

 forearm at right angles to the arm, the tip of the olecranon and the two condyles 



Fig. 301. 



B 



Posterior view of elbow, showing relative position of condyles and olecranon. A, in extension ; B, in flexion. 



are on the same plane as the back of the upper arm. In extreme extension it is 

 about one-sixteenth of an inch or less above a straight transverse line joining the 

 two condyles ; in full flexion it is anterior to them. In front the tip of the coronoid 

 process can be felt with difficulty in non-muscular subjects. The shaft is subcutaneous 

 through its entire length. The styloid process is a half- inch nearer the forearm than 

 the styloid process of the radius. It is most distinct in full supination, and is found 

 at the inner and posterior aspect of the wrist. In full pronation the head of the ulna 

 becomes prominent posteriorly. 



THE RADIUS. 

 The radius includes a shaft and two extremities. 



The upper extremity consists of a head and neck. The head ^ is a circular 

 enlargement with a shallow depression on top to articulate with the capitellum, and 



-* Capitulum. 



