RADIO-ULNAR JOINTS 205 



be noticed that the head of the radius does not fit accurately upon 

 the capitulum in all positions of the elbow joint. In extreme extension 

 and extreme flexion of the elbow it is only partially in contact with it. 

 Therefore the semi-flexed condition of the elbow joint places the radius 

 in the most favourable position for free and precise movement at the 

 proximal radio-ulnar joint (Figs. 86, 87, 88, 91, 92, 93). 



At the distal radio-ulnar joint the distal end of the radius revolves 

 around the distal end of the ulna. It carries the hand with it, and describes 

 the arc of a circle, the centre of which corresponds to the attachment of the 

 articular disc to the distal end of the ulna. As the movement occurs the 

 articular disc 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. 

 They are aided by the long abductor and the long extensor of the thumb. 

 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, on account of the preponderating influence of the biceps. 



Dissection. The annular ligament should be cut through, 

 and the oblique cord and the interosseous membrane 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 triquetral bone, to. which it is attached by 

 an articular capsule. 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 capsule would be quite incapable by itself of with- 



