f>8 



DISSECTION OF FRONT OF FOREARM. 



insertion : 



parts 

 around it 



use on 

 fingers and 

 wrist. 



How fingers 

 are bent. 



Long flexor 

 of thumb : 



origin ; 



insertion ; 

 parts above 



and beneath 

 it; 



Pronator 

 quadratus 



is deep in 

 position ; 



Anterior in- 



terosseous 



artery. 



fleshy bell} 7 , and ends in tendons which, passing beneath the 

 annular ligament, are inserted into the last phalanges of the fingers 

 (fig. 32, p. 78). The portion of the muscle furnishing the tendon 

 to the index finger is separated from the rest by a layer of areolar 

 tissue, and arises chiefly from the interosseous membrane. 



Lying over the muscle are the ulnar vessels and nerve, the 

 superficial flexor of the fingers, and the flexor carpi ulnaris. The 

 deep surface rests on the ulna and the pronator quadratus muscle. 

 The outer border touches the flexor longus pollicis and the anterior 

 interosseous vessels and nerve. 



Action. The muscle bends the joints of the fingers and the wrist ; 

 but it does not act on the last phalanx till after the second has been 

 moved by the flexor sublimis. 



The fingers are usually bent in the following order : firstly, the 

 articulation between the first (proximal) and the middle phalanges ; 

 secondly, the last phalangeal joint ; and thirdly, the metacarpo- 

 phalangeal. 



The FLEXOR LONGUS POLLICIS (fig. 26, B) arises from the anterior 

 surface of the radius below the oblique line (fig. 25), as low as the 

 pronator quadratus, and from the outer part of the interosseous 

 membrane ; it is also joined in most cases by a distinct slip arising 

 in common with the flexor sublimis digitorum either from the internal 

 condyle of the humerus or the coronoid process of the ulna. The 

 fleshy fibres descend to a tendon, which is continued beneath the 

 annular ligament, and is inserted into the last phalanx of the thumb. 



The greater part of the muscle is covered by the flexor sublimis 

 digitorum ; and the radial vessels rest on it for a short distance 

 below. It lies on the radius and the pronator quadratus. To the 

 inner side is the flexor profundus digitorum. 



Action. This muscle is the special flexor of the last joint of the 

 thumb, but it also aids in bending the other joints of that digit and 

 the wrist. 



The PRONATOR QUADRATUS (fig. 26, D) is a flat muscle cover- 

 ing the lower fourth of the bones of the forearm. It arises from 

 the anterior surface of the ulna, where it is widened by a 

 somewhat linear and partly tendinous origin, and is inserted into 

 the fore and inner parts of the radius for about two inches (fig. 25). 



The anterior surface is covered by the tendons of the flexor 

 muscles of the digits, and by the radial vessels ; and the posterior 

 surface rests on the radius and ulna with the intervening membrane, 

 and on the interosseous vessels and nerve. Along its lower border 

 is the arch formed by the anterior carpal arteries. 



Action. The end of the radius is moved inwards over the ulna by 

 this muscle, and the hand is pronated. 



The ANTERIOR TNTEROSSEOUS ARTERY (fig. 26, e) is continued on 

 the front of the interosseous membrane between the two flexors or 

 in the fibres of the flexor profundus digitorum, till it reaches an 

 aperture in the membrane near the upper border of the pronator 

 quadratus. At that spot the artery turns from the front to the 

 back of the limb, and descends to the back of the carpus, where 



