THE MIDDLE PALMAR REGION 217 



The palmar interossei are three in number, are adductors, 

 and each rises from the lateral surface of the metacarpal of 

 the finger on which it acts. They terminate like the dorsal 

 tendons. The first belongs to the ulnar side of the index, 

 the second and third to the radial sides of the ring and little 

 fingers. 



The lumbricales are four small muscles, not always wells 

 defined. They rise from the tendons of the flexor profundus 

 digitorum; the first and second, from the radial side and palmar 

 surface of the tendons of the index and middle fingers respec- 

 tively; the third from the adjoining sides of the tendons of 

 the middle and ring fingers; and the fourth from the adjoining 

 sides of the tendons of the ring and little finger. They pass to 

 the radial side of the corresponding fingers and opposite the 

 metacarpophalangeal articulation; each tendon is inserted into 

 the tendinous expansion of the extensor communis digitorum, 

 covering the dorsal aspect of each finger. 



Nerves of Hand Muscles. Abductor pollicis, opponens pollicis, 

 outer head of the flexor brevis pollicis, and outer two lumbri- 

 cales are supplied by the median nerve. The palmaris brevis, 

 muscles of the little finger, inner two lumbricales, all the inter- 

 ossei, adductores pollici, inner head of the flexor brevis pollicis, 

 are supplied by the ulnar nerve. 



Actions of Muscles of the Forearm and Hand. Pronation 

 by the pronator teres and quadratus and flexor carpi radialis 

 slightly; pronator teres flexes the forearm; can only pronate 

 when the radius is intact. 



Supination by the supinator brevis, biceps, and supinator 

 longus ; the latter is a flexor of the elbow and brings the forearm 

 into midsupination. Radial extensors of the wrist flex the 

 elbow; others from the external condyle extend. Flexion 

 of the wrist by the flexor carpi ulnaris and radialis, by the 

 flexors of the fingers and palmaris longus. 



Extension of the wrist by the extensor carpi ulnaris, the two 

 radial extensors, and extensors of the fingers. 



Abduction of the wrist by the radial flexor and radial extensors 

 and extensors of the thumb. 



Adduction of the wrist by the flexor and extensor carpi ulnares. 

 The flexor carpi radialis and extensor carpi ulnaris act on the 

 radiocarpal joint; the flexor carpi ulnaris and radial extensors on 

 the midcarpal joint. 



