158 THE UPPER EXTREMITY 



discus articularis to the distal end of the ulna. In this movement the 

 discus articularis moves with the radius, and travels dorsally on the distal 

 end of the ulna in supination, and towards the volar surface in pronation. 



But the question may be asked, does the ulna move during pronation 

 and supination ? When the elbow-joint is extended to its fullest extent the 

 ulna remains almost immovable. When, however, pronation and supination 

 are conducted in the semi-flexed limb, the ulna does move. A small 

 degree of lateral movement at the elbow-joint is allowed, and the distal 

 end of the ulna during pronation is carried slightly dorsally and laterally, 

 and in the reverse direction during supination. 



The muscles which are chiefly concerned in producing supination of the 

 forearm are the biceps brachii, the brachio-radialis, and the supinator. 

 The biceps brachii, from its insertion into the dorsal part of the tuberosity 

 of the radius, is placed in a very favourable position, in so far as its supinat- 

 ing action is concerned. The muscles which act as pronators of the limb are 

 the pronator teres, the pronator quadratus, and, to a certain extent, the 

 flexor carpi radialis. The pronator teres, from its insertion into the 

 point of maximum lateral curvature of radius, can exercise its pronating 

 action to great advantage. The balance of power is in favour of the 

 supinators, and this is due to the preponderating influence of the biceps. 



Dissection. The annular ligament should be cut through, and the 

 oblique cord and the membrana interossea should be divided proximo- 

 distally. By drawing the radius laterally and opening the capsule of the 

 distal radio-ulnar joint, the proximal surface of the discus articularis of 

 the wrist will be displayed and its attachments more fully appreciated. 



ARTICULATIONES CARPE^E (CARPAL JOINTS). 



In the carpus two joints are recognised 



1. Articulatio ossis pisiformis. 



2. Articulatio intercarpea. 



Pisiform Joint. The pisiform bone articulates with the 

 volar surface of the os triquetrum to which it is attached by a 

 capsular ligament. The cavity of the pisiform joint is quite 

 distinct from those of the adjacent joints. 



The dissector has previously noted that the tendon of the 

 flexor carpi ulnaris is inserted into the pisiform bone, and 

 as the capsular ligament would be quite incapable by itself of 

 withstanding the strain to which this muscle subjects the 

 articulation, certain accessory bands are provided which 

 anchor the pisiform firmly in place they are the piso-hamate 

 and the piso-metacarpal bands. The former passes from the 

 distal end of the pisiform to the hook of the os hamatum, 

 and the latter attaches the pisiform to the proximal ends of 

 the fourth and fifth metacarpal bones. 



