386 



THE MUSCULAR SYSTEM. 



A 1 



bones on their volar surfaces (Fig. 351, p. 392). The chief tendon is that to the 

 second metacarpal bone. 



The muscle is superficial except near its insertion. Its tendon, in the distal 

 half of the forearm, is an important guide to the radial vessels, which are placed 

 to its radial side. After passing beneath the transverse carpal ligament the 

 tendon is concealed by the origins of the short muscles of the thumb, and is crossed, 

 from medial to lateral side, by the tendon of the flexor pollicis longus. Besides the 

 mucous sheath enveloping the tendon beneath the ligament, a mucous bursa is 

 placed beneath the insertion of the tendon. 



Nerve-Supply. Median nerve (C. 6.). 



Actions. This muscle has a threefold action. It is mainly a flexor of , the elbow and wrist, 

 but it also acts as an accessory pronator of the forearm. 



M. Palmaris Longus. The palmaris longus arises also from the common 

 flexor tendon from the medial epicondyle of the humerus, from the fascia over it, 



and from intermuscular septa 

 on each side. 



It forms a short fusiform 

 muscle, which ends, in the 

 middle of the forearm, in a 

 7 long flat tendon. This pierces 

 the deep fascia, near the wrist, 

 E and passing over the trans- 

 F verse carpal ligament, is in- 

 serted (1) into the surface of 

 the transverse carpal ligament, 

 and (2) into the apex of the 

 thick central portion of the 

 palmar aponeurosis. A ten- 

 dinous slip is frequently sent 

 to the shorb muscles of the 

 thumb and the fascia covering 

 them. 



The palmaris longus is the 



A, PRONATOR TERES (insertion); B, FLEXOR CARPI RADIALIS; C, FLEXOR sma ll es t muscle of the forearm. 



DIOITORUM SUBLIMIS J D, PALMARIS LONGUS ; E, FLEXOR CARPI ULNARIS J _ , , . - , . - 



F, FLEXOR DIOITORUM PROFUNDUS ; G, EXTENSOR CARPI ULNARIS ; In til 6 QlStal tillm 01 the 

 H, EXTENSOR POLLICIS LONGUS ; I, EXTENSOR DIGITORUM COMMUNIS AND forearm its tendon is placed 



EXTENSOR DIGITI QUINTI PROPRIUS J J, ABDUCTOR POLLICIS LONGUS ; K, dirPCtlv Qvpr 4-1^ TTlPfHlTl 



EXTENSOR CARPI RADIALIS BREVIS ; L, EXTENSOR CARPI RADIALIS LONGUS ; L ' U V 



M, BRACHIORADIALIS. a, Radius ; b, Interosseous membrane ; c, Ulna, nerve, along the radial border 



1, Superficial ramus of radial nerve ; 2, Radial artery ; 3, Volar inter- Q ^g tendons of the fleXOr 



osseous artery; 4, Volar interosseous nerve (underneath flexor pollicis -, , VT " 



longus) ; 5, Median nerve ; 6, Ulnar artery ; 7, Ulnar nerve ; 8, Dorsal dlgl imiS. 



interosseous artery ; 9, Dorsal interosseous nerve. 



The palmaris longus is the 



most variable muscle in the body, and is often absent (10 per cent). 

 Nerve-Supply. Median nerve (C. 6.). 

 Actions. The muscle assists in flexion of the elbow and wrist. It also by tightening the 



palmar aponeurosis deepens the hollow of the hand and helps to flex the fingers. 



M. Flexor Carpi Ulnaris. The flexor carpi ulnaris muscle has a double 

 origin, from the humerus and from the ulna. (1) It arises from the common tendon 

 attached to the medial epicondyle of the humerus, from the fascia over it, and from 

 a lateral intermuscular septum. (2) By means of the deep fascia of the forearm it 

 obtains an attachment to the medial border of the olecranon and the dorsal margin 

 of the ulna in its proximal three-fifths. 



The fleshy fibres join a tendon which lies on the anterior border of the muscle 

 and is inserted into the pisiform bone, and in the form of two ligamentous ban del 

 (piso-hamate and piso-metacarpal) into the hamulus of the os hamatum, and thel 

 proximal end of the fifth metacarpal bone (Fig. 351, p. 392). 



The muscle is superficially placed along the medial border of the forearm. It 

 conceals the flexor digitorum profundus muscle, the ulnar nerve (which enters! 



PIG. 344. DISTAL SURFACE OF A SECTION ACROSS THE EIGHT 

 FOREARM IN THE MIDDLE THIRD. 



