194 THE SUPERIOR EXTREMITY 



first or most lateral dorsal interosseous muscle, the tendon is 

 inserted into the lateral side of the base of the first phalanx, 

 and also into the lateral margin of the dorsal expansion of the 

 extensor tendon of the index. The second and third dorsal 

 interosseous muscles are inserted in a similar manner, one on 

 each side of the base of the first phalanx of the middle finger; 

 whilst the fourth has a corresponding insertion upon the medial 

 aspect of the base of the first phalanx of the ring finger. 



The first dorsal interosseous muscle is frequently termed 

 the abductor indicts ; and between its two heads of origin the 

 radial artery enters the palm. Between the heads of the other 

 three muscles the small perforating arteries pass. 



In addition to acting as adductors or abductors of the 

 fingers the interossei flex the metacarpo-phalangeal joints and 

 help to extend the interphalangeal joints (see p. 178). The 

 interosseous muscles are supplied by the deep branch of the 

 ulnar nerve. 



Tendon of the Flexor Carpi Radialis. The tendon of the 

 radial flexor of the carpus should now be traced through the 

 groove on the volar aspect of the os multangulum majus to its 

 insertion into the base of the metacarpal bone of the index 

 finger. It presents also a minor attachment to the base of the 

 middle metacarpal bone. On its way to its insertion it passes 

 behind the tendon of the flexor pollicis longus. 



Dissection. All the muscles around the elbow joint should 

 be removed. As the brachialis and the triceps are raised from 

 the anterior and posterior aspects of the articulation, some care 

 is required to avoid injury to the anterior and posterior parts of 

 the capsule. It is advisable to remove the supinator last, because 

 it is only when that muscle is completely isolated that a proper 

 idea of its attachments and mode of action can be obtained. 

 Before it is removed its attachments and actions must be studied. 



M. Supinator (O.T. Supinator Brevis). The supinator 

 muscle envelops the proximal part of the body and the neck 

 of the radius, covering it completely, except on its medial 

 side (Figs. 64, 78). It arises from the deep depression 

 distal to the radial notch of the ulna, and also from the 

 radial collateral ligament of the elbow and the annular 

 ligament of the radius. From their origin the fibres sweep 

 round the dorsal, lateral, and volar surfaces of the radius, and 

 clothe its body as far distally as the insertion of the pronator 

 teres. The dorsal interosseous nerve supplies the muscle, 

 traverses its substance, and separates it into two layers. 



