200 THE SUPERIOR EXTREMITY 



articular facet on the extreme lateral part of the proximal 

 surface of the triquetral bone. Two interosseous ligaments 

 stretch across the narrow intervals between the three bones 

 one on each side of the lunate bone and complete the 

 carpal surface. The carpal surface thus formed is convex 

 in all directions. Further, it should be observed that the 

 articular surface extends distally to a greater extent on the 

 dorsal than on the volar aspect. 



The proximal surface or socket (Fig. 97) is elongated from 

 side to side, and concave in all directions. The greater 

 part of it is formed by the distal end of the radius, but, 

 on the medial side, the articular disc of the distal radio- 

 Head of ulna 



Styloid process 

 of ulna 



Surface for, 

 navicular bone ^-_ -,,< 



Apex of articular 



Groove for tendon of ext. ^^ I ' . 



pollicislongus Surfacefor ?* 



lunate bone 



FIG. 95. Carpal Articular Surfaces of the Radius and of the Articular 

 Disc of the Wrist. 



ulnar joint also enters into its construction. The distal 

 articular surface of the radius extends further distally on its 

 dorsal and lateral sides than on its volar and medial sides, 

 and it is divided by a low ridge into a lateral triangular and 

 a medial quadrilateral facet. The lateral facet, in the 

 . ordinary position of the hand, is in contact with the greater 

 extent of the proximal articular surface of the navicular bone. 

 The medial facet of the radius, together with the articular 

 disc, forms a much larger surface, triangular in outline, 

 which is opposed to the proximal articular surface of the 

 lunate bone. When the hand is placed in line with the 

 forearm no part of the proximal articular surface is allotted 

 to the triquetral bone : its small articular facet rests against 

 the medial part of the capsule of the joint. When the hand 

 is moved medially (i.e. adducted), however, the triquetral 

 bone travels laterally, and its articular surface comes into 



