118 PRACTICAL ANATOMY. 



three borders anterior, posterior, and internal and 

 three surfaces anterior, posterior, and external. The 

 anterior border, also called the oblique line, starts below 

 the tuberosity and terminates at the styloid process ; the 

 posterior border, rounded, terminates below in the pos- 

 terior portion of the styloid process ; the internal border 

 is sharp, and affords attachment to the interosseous liga- 

 ment. The surfaces afford attachment to muscles. The 

 lower end of the radius is a cuboidal mass of bone, which 

 presents a posterior, an outer, an anterior, an inner, and 

 an inferior surface. The posterior surface, quadrilateral 

 in form, is convex from side to side, and from above 

 downward. It presents three grooves, which run in the 

 direction of the axis of the bone. They are an outer, 

 broad and shallow, which lodges the tendons of the 

 extensor carpi radialis longior and brevior ; the middle 

 groove, narrow and deep, for the tendon of the extensor 

 secundi internodii pollicis ; the inner groove, broad and 

 shallow, for the extensor tendons of the index and little 

 fingers and the common extensors. 



The outer surface is narrow and triangular, and ter- 

 minates below in a strong, conical process of bone, the 

 styloid process. It presents two grooves, an anterior, 

 for the tendon of the extensor ossis metacarpi pollicis, 

 and a posterior, for the tendon of the extensor primi 

 internodii pollicis. The anterior surface is broad, con- 

 cave from above downward, flattened from side to side ; 

 it serves for the attachment of the pronator quadratus 

 muscle. The inner surface, quadrilateral and flattened, 

 presents a slight concave, articular surface for the side 

 of the head of the ulna. This articular surface is called 

 the sigmoid cavity of the radius. The inferior surface is 

 entirely articular, and triangular in outline. Its base is 

 at the inner surface and its apex at the styloid process ; 



