90 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



triangular fibrocartilage. Posteriorly between the head and 

 styloid process is a groove for the tendon of the extensor carpi 

 ulnaris. 



The head has two articular surfaces an inferior one, upon 

 which the triangular fibrocartilage plays, and an outer narrow 

 convex one, for the sigmoid cavity of the radius. With the 

 hand supine the styloid process projects at the inner and back 

 part of the wrist; if pronated, the outer and forepart of the 

 ulnar head is prominent between the tendons of the extensor 

 carpi ulnaris and extensor minimi digiti. 



The Radius 



The radius is the outer and smaller of the two bones of 

 the forearm. It articulates with the humerus, ulna, scaphoid, 

 and semilunar bones, and presents for examination a shaft 

 and two extremities. 



The superior extremity, or head (eminentia capitata), is 

 disk-shaped. On its summit is a shallow^ depression for the 

 capitellum of the humerus. Its circumference is convex, 

 broadest internally, where it rotates in the small sigmoid cavity 

 of the ulna within the orbicular ligament. The head is sup- 

 ported by a neck, round and smooth, which presents behind 

 a perpendicular ridge for part of the insertion of the supinator 

 brevis. 



The shaft is larger below than above, slightly curved, and 

 convex outward and backward. Anterointernally below the 

 neck is the bicipital tuberosity, rough posteriorly for the inser- 

 tion of the biceps, and smooth in front for a bursa. Below 

 this tuberosity the shaft has three surfaces and three borders. 



The anterior border extends from the tuberosity to the base 

 of the styloid; its upper part runs downward and outward 

 to the middle of the bone, being called the anterior obliqvt 

 line, and gives attachment to the supinator brevis, flexor 

 longus pollicis, and flexor sublimis. The pronator radii teres 

 is attached at the middle of the border, which from this point 

 descends vertically. 



The posterior border runs from the back of the neck to the 

 posterior part of the base of the styloid. It is well marked 

 only in its middle third. 



The internal or inter osseous border becomes prominent below, 



