THE MUSCULAR SYSTEM. 



153 



oblique line of the radius, from the insertion of the pronator 

 radii teres, to the tubercle; each tendon divides at the base of 

 the first phalanges to allow the passage of the tendon of the 

 flexor profundus digitorum ; insertion, 

 into the lateral margins of the second 

 phalanges by four tendons ; action, 

 flexes the second phalanges ; nerve, 

 median. 



Anterior Deep Layer. 



FLEXOR PROFUNDUS DIGITORUM 

 (PERFORANS). Origin., from the inner 

 side of the coronoid process, and from 

 the upper two-thirds of the front and 

 inner aspect of the shaft of the ulna, 

 between the brachialis anticus above 

 and the pronator quadratus below ; 

 insertion, by four tendons into the 

 bases of the last phalanges, perforating 

 the tendons of the flexor sublimis ; 

 action, flexes the phalanges ; nerves, 

 the anterior interosseous and the ulnar. 



FLEXOR LONGUS POLLICIS. Origin, 

 from the upper two-thirds of the shaft 

 of the radius and from the interosseous 

 membrane ; insertion, into the base of 

 the last phalanx of the thumb ; action, 

 flexes the phalanges ; nerve, the ante- 

 rior interosseous. 



PRONATOR QUADRATUS. Origin, 

 anterior border of the ulna and from 

 the oblique line of the lower fourth 

 of the anterior aspect of the ulna ; 

 insertion, into the lower fourth of the 

 front and outer border of the shaft of 

 the radius ; action, pronates the hand ; 

 nerve, anterior injsrosseous. 



FIG. 99. 



Muscles of forearm: 

 1, biceps; 2, brachialis 

 anticus; 3, triceps; 4, 

 supinator longus; 5, ex- 

 tensor carpi radialis lon- 

 gior; 6, extensor carpi 

 radialis brevior; 8, ex- 

 tensor communis digi- 

 torum; 12, extensor carpi 

 ulnaris; 13, 14, extensors 

 of thumb. 



Radial Region. 

 SUPINATOR LONGUS. Origin, from 



the upper two- thirds of the external condyloid ridge of the 

 humerus and the external intermuscular septum ; insertion, into 

 the base of the styloid process of the radius ; action, supinates 

 the hand ; nerve, musculo-spiral. 



