BOXES OF THE UrPER LIMB. 



quadrilateral, presents inferiorly a large surface, wliich articulates -with 

 the carpus, and internally a small one, which articulates with the ulna. 

 The carpal articular surface, slightly concave, is divided by a line into 

 a quadrilateral internal part, which articulates with the semilunar bone, 

 and a triangular external part, which articulates with the scaphoid 

 bone. The ulnar articular surface is placed at a right angle with the 

 inferior surface ; it is concave from before backwards, forming a semi- 

 hinar cavitij, in whicli the rounded lower end of the ulna plays. At 

 the external angle of the inferior surface a part projecting downwards, 

 called the sfi/Ioid process, gives attachment to the external lateral liga- 

 ment of the wrist joint, while the anterior and posterior margins are 



Fi? 





m 



m 



G 



73. — Right Radius from before. 

 74. — Right Radius from behind. 



m 



20- 



(A.T.)i 



1, head, showing the hollow above for the humerus, 

 and the vertical surface surrounding it for the ulnar 

 articulation ; 2, the neck ; 3, the tubercle ; 4, is 

 oi)posite to the oblique line : 5, interosseous ridge ; 

 the shaded pai-t near 5 marks the slight hollow in 

 which the flexor longus pollicis muscle lies ; 6, car- 

 jial articular surface ; 7, styloid jn-ocess ; 8, the 

 articular hollow for the lower end of the ulna ; 9, 

 mark of the attachment of the pronator radii teres ; 

 10 and 11, oblique impressions of the e.xtensor 

 longus digitorum and extensor ossis metacaqji 

 IJollicis ; between 7 and 8, dorsal grooves for the 

 tendons of the extensor muscles. 



likewise rough and prominent for other 

 ligaments. On its external posterior as- 

 pects the inferior extremity of the radius 

 is marked by grooves, which transmit the 

 extensor tendons. Thus, on the external 

 border, is a flat groove directed down- 

 wards and forwards, which lodges the 

 extensor ossis metacarpi and extensor 

 primi internodii pollicis ; and on the 

 posterior surface are three grooves, the 

 middle one of which, oblique and nar- 

 row, and with prominent borders, lodges 

 the extensor secundi internodii pollicis ; 

 while of the two others, which are broad 

 and shallow, the external, subdivided by 

 a slight mark, gives passage to the cx- 

 tensores carpi radiales longior and bre- 



vior, and the internal transmits the extensor communis digitorum and 



extensor indicis. 



THE ULNA. 



The ulna is the internal of the two bones of the forearm. It is 

 longer than the radius by the extent of the olecranon process. It is 

 inclined downwards and outwards fi'om the humerus in such a direc- 

 tion that a straight line passing fi-om the great tuberosity of the 

 humerus downwards through the capitellum would touch the lower 

 end of the ulna. 



The ulna articulates with the humerus and the radius : in the 



