154 



THE SKELETON 



tuting the oblique line of the radius, gives origin to the radial head of the flexor 

 digitorum suhlimis, limits the insertion of the supinator above, and the origin 

 of the flexor pollicis longus below. The volar border separates the volar from 

 the lateral surface. The dorsal border extends from the back of the tuberosity to 

 the prominent middle tubercle on the posterior aspect of the lower extremity. 

 Separating the lateral from the dorsal surface, it is well marked in the middle 

 third, but becomes indistinct above and below. 



Surfaces. — The volar (or anterior) surface is narrow and concave above; broad, 

 flat, and smooth below. The upper two-thirds is occupied chiefly by the flexor 

 pollicis longus and a little less than the lower third by the pronator quadratus. Near 



Fig. 182. — Articular Facets on the Lower End of Left Radius and Ulna. 



Posterior 



Radius 



Ulna 



For navicular 

 For lunate 



Styloid process of ulna 



Head of ulna : it articulates with 

 the interarticular fibro-cartilage 

 of the wrist-joint 



Anterior 



the junction of the upper and middle thirds of the volar surface is the nutrient fora- 

 men, directed upward toward the proximal end of the bone. It transmits a 

 branch of the volar interosseous artery. The lateral surface is rounded above 

 and affords insertion to the supinator; marked near the middle by a rough, low, 

 vertical ridge for the pronator teres; smooth below, where the tendons of the exten- 

 sor carpi radialis longus and hrevis lie upon it, and where it is crossed by the 

 abductor pollicis longus and extensor pollicis hrevis. The dorsal (or posterior) 

 surface, smooth and rounded above, is covered by the supinator; grooved longi- 

 tudinally in the middle third for the abductor pollicis longus and the extensor pollicis 



Fig. 183. — Dorsal View of the Lower End op the Radius and Ulna. 



Radius 



Insertion of brachio-radialis / ' 



Abductor pollicis longus and '' 



ext. pollicis brevis 

 Extensor carpi radialis longus 



and brevis 

 Tubercle for posterior annular — I*''- 

 ligament 

 Extensor pollicis longus ilild 



Styloid process 



Ulna 



Ext. digitorum communis and 

 extensor indicis proprius 



Extensor quinti digiti proprius 

 lies in the groove between the 

 radius and ulna 



Extensor carpi ulnaris 



Styloid process 



brevis; the lower third is broad, rounded, and covered by tendons. The line which 

 forms the upper Hmit of the impression for the abductor pollicis longus is known 

 as the posterior oblique line. 



The lower extremity of the radius is quadrilateral; its carpal surface [facies 

 articularis carpeaj is articular and divided by a ridge into a medial quadrilateral 

 portion, concave for articulation with the lunate bone; and a lateral triangular 

 portion, extending onto the styloid process for articulation with the navicular 

 (scaphoid) bone. The medial surface, also articular, presents the ulnar notch 

 (sigmoid cavity) for the reception of the rounded margin of the head of the ulna. 

 To the border separating the ulnar and carpal articular surfaces the base of the 



