270 DISSECTION OF THE FRONT OF THE FOREARM. 



the muscles on the front of the forearm, and furnishes a cutaneous offset 

 to the hand. 



a. Muscular offsets leave the trunk of the nerve near the elbow, and 

 are distributed to all the muscles of the superficial layer except the flexor 

 carpi ulnaris ; in addition, the nerve supplies the deep layer through the 

 interosseous branch (p. 271), except the inner half of the flexor profun- 

 dus digitorum. 



b. The cutaneous palmar branch ( 3 ) arises in the lower fourth of the 

 forearm ; it pierces the fascia near the annular ligament, and crosses over 

 that ligament to reach the palm of the hand. 



The RADIAL NERVE is the smaller of the two branches into which the 

 musculo-spiral divides at the elbow. This nerve is placed along the outer 

 border of the limb, under cover of the supinator longus (fig. 80), and on 

 the outer side of the radial artery till within three inches of the wrist, 

 where it becomes cutaneous at the posterior border of the supinator tendon. 

 On the surface of the limb it divides into two branches, which are dis- 

 tributed on the dorsum of the hand, and digits (3J) (p. 262). No muscular 

 offset is furnished by the nerve. 



Dissection (fig. 81). To examine the deep layer of muscles it will be 

 necessary to draw well over to the radial side of the forearm the pronator 

 teres ; to detach the flexor sublimis from the radius, and to remove its 

 fleshy part. The areolar tissue is to be taken from the deep muscular fibres ; 

 and the anterior interosseous vessels and nerve, which lie on the interosse- 

 ous membrane, and are concealed by the muscles, are to be traced out. 



Above the ends of the forearm-bones the arch of the anterior carpal 

 arteries may be defined. 



DEEP LAYER OF MUSCLES. Only three deep muscles are present on the 

 front of the forearm. One lies on the ulna, and is the deep flexor of the 

 fingers ; a second covers the radius, viz., the long flexor of the thumb ; 

 and the third is the pronator quadratus, which lies beneath the other two, 

 near the lower end of the bones. 



The FLEXOR DIGITORUM PROFUNDUS vel PERFORANS (fig. 81, C ) arfses 



from the anterior and inner surfaces of the ulna for three-fourths of the 

 length of the bone ; from the inner half of the interosseous ligament for 

 the same distance ; and from an aponeurosis common to the muscle and 

 the flexor carpi ulnaris. The muscle has a thick fleshy belly, and ends in 

 tendons which, united together, pass beneath the annular ligament, and are 

 inserted into the last phalanges of the fingers. 



The cutaneous surface of the muscle is in contact with the ulnar nerve 

 and vessels, the superficial flexor of the fingers, and the flexor carpi ulna- 

 ris. The deep surface rests on the ulna and the pronator quadratus mus- 

 cle. The outer border touches the flexor pollicis longus and the anterior 

 interosseous vessels and nerve ; and the inner is connected by aponeurosis 

 to the posterior margin of the ulna. 



Action. The muscle bends the last 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 approximated and the joints bent in the following order : 

 first, the articulation between the metacarpal and the middle phalanx is 

 flexed, secondly, the last phalangeal joint, arid thirdly the metacarpo-pha- 

 langeal. 



The FLEXOR LONGUS POLLICIS (fig. 81, B ) arises from the hollowed an- 

 terior surface of the radius, as low as the pronator quadratus ; from the 



