98 



THE BOXES OF THE UPPER LIMB. 



J 



margin. It presents on its summit a depression, which articulates with the 



capitellum of the humerus, and is surrounded by a convex part, broadest internally 



where it glides upon the groove internal to 

 the capitellum. The smooth, short, cylin- 

 drical surface of the vertical margin, likewise 

 broadest internally, rotates in the small sig- 

 moid cavity of the ulna, and within the 

 orbicular ligament. The head is supported 

 on a constricted portion, named the neck. 



The shaft or body is larger below than 

 above, and slightly curved, with the convexity 

 directed outwards and backwards. On its 

 antero -internal aspect superiorly, where it is 

 continuous with the neck, is the bicipital 

 titberositi/, to the posterior rough portion of 

 which is attached the tendon of the biceps 

 muscle. Below the bicipital tuberosity the 

 shaft has three surfaces, of which the external 

 is only indistinctly marked off from the others 

 by smooth, rounded anterior and posterior 

 borders, while the anterior and posterior sur- 

 faces are separated in their middle three- 

 fifths by a sharp, prominent internal border 

 which gives attachment to the interosseous 

 membrane. The anterior surface is limited 

 above by the prominent anterior oblique line, 

 running from the lower part of the tube- 

 rosity downwards and outwards to form the 

 anterior border, and giving origin to a part 

 of the flexor sublimis digitorum ; below this 

 the surface is grooved longitudinally for the 

 flexor longus pollicis muscle ; and at the 

 lower end it is expanded, and presents a 

 flattened impression for the insertion of the 

 pronator quadratus, which also occupies a 

 small triangular surface on the inner side of 

 the bone in its lower fifth : above the middle 

 of the anterior surface is the foramen for the 

 medullary artery, directed upwards into the 

 bone. The posterior surface is marked at the 

 junction of its upper and middle thirds by 

 the posterior oblique line, which limits supe- 

 riorly the impression of the extensor ossis 

 metacarpi pollicis ; below this is another 

 small oblique impression for the extensor 

 brevis pollicis. The external surface is convex 

 transversely as well as longitudinally, and is 

 marked near the middle, at its most prominent 

 part, by a rough impression for the insertion 



of the pronator teres. Above this, the area between the anterior and posterior 



oblique lines gives insertion to the supinator brevis. 



The lower extremity of the radius, broad and thick, presents inferiorly a 



large surface which articulates with the carpus, and internally a small one which 



Fig. 97. RIGHT RADIUS : POSTERIOR VIEW 

 (Drawn by T. W. P. Lawrence.) f 



