33 2 



APPLIED ANATOMY. 



The lower or radiocarpal articular surface slopes downward and outward to end 

 in the styloid process, which is thereby placed lower than the styloid process of the 

 ulna. The articular surface is divided into two facets: the outer is the smaller, 

 is triangular in shape, and articulates with the naviadar {scaphoid) bone; the 

 inner or larger is quadrilateral and articulates with the lunate {semilunar} bone. 

 The styloid process at its base or upper outer portion has inserted into it the tendon 

 of the brachioradialis muscle. To its tip is attached the external lateral ligament. 



The Ulna. The lower extremity of the ulna is rounded in shape, forming its 

 head, with the styloid process projecting downward on its inner and posterior aspect. 

 To its tip is attached the internal lateral ligament. On its outer side is a rounded 

 smooth surface for articulation with the ulnar notch of the radius. The inferior 

 or articular surface is flat and rests on the flat interarticular fibrocartilage. 



The navicular (scaphoid), lunate (semilunar), cuneiform, and pisi- 

 form bones form the first row of the carpal bones. The pisiform rests on the 

 anterior surface of the cuneiform and does not enter into the articulations between 

 the hand and bones of the forearm. 



The navicular and lunate articulate directly with the lower end of the radius, 

 but the cuneiform articulates with the under surface of the triangular interarticular 

 fibrocartilage. 



THE INFERIOR RADIO-ULNAR ARTICULATION. 



The joint between the lower ends of the radius and ulna embraces not only the 

 portion between these two bones but also that between the lower end of the ulna and 



Radiu 



Radiocarpal (wrist) joint 



External lateral lig 



Scaphoid ^ 

 igament 1 



Ulna 



Pronator quadratus 



Inferior radio- ulnar joint 



Triangular fibrocartilage 



Semilunar 



Internal lateral ligament 



Cuneiform 



Flexor carpi ulnaris tendon 



Pisiform 



FIG. 341. The wrist- joint and inferior radio-ulnar articulation. 



the upper surface of the triangular fibrocartilage. This latter is attached by its apex 

 to a depression on the outer side of the root of the styloid process of the ulna, and 

 by its base to the rough line on the radius separating the radio-ulnar from the radio- 

 carpal articulation (Fig. 341). 



The Interarticular Triangular Fibrocartilage. This serves as the main 

 bond of union between the lower ends of the radius and ulna. It is strong and 

 blends with the internal lateral ligament. Thus the hand has an attachment to the 

 inner side of the radius by means of the internal lateral ligament and triangular 

 cartilage. 



