154 HUMAN ANATOMY. 



EXTENSOR CARPI EADIALIS LONGIOR. Origin , from the 

 lower third of the external condyloid ridge of the humerus, from, 

 the common tendon of the extensor muscles of the forearm from 

 the external condyle, and the intermuscular septum; insertion, 

 into the radial side of the base of the metacarpal bone of the in- 

 dex finger; action, extends the wrist; nerve, musculo-spiral. 



EXTENSOR CARPI EADIALIS BREVIOR. Origin, from the 

 common tendon, from the external condyle of the humerus, the 

 external lateral ligament, and the intermuscular septum; inser- 

 tion, into the base of the metacarpal bone of the middle finger 

 on its radial side; action, extends the wrist; nerve, posterior 

 interosseous. 



Posterior Superficial Layer. 



EXTENSOR COMMUNIS DIGITORUM. Origin, from the ex- 

 ternal condyle of the humerus, the deep fascia, and the inter- 

 muscular septa; insertion, by four tendons into the second and 

 third phalanges of all the fingers (at the first phalanx they 

 receive the insertion of the lumbricales and.interossei) ; action, 

 extends the fingers ; nerve, posterior interosseous. 



EXTENSOR MINIMI DIGITI. Origin, from the common ten- 

 don from the external condyle and the intermuscular septum; 

 insertion, into the second and third phalanges of the little finger ; 

 action, extends the little finger; nerve, posterior interosseous. 



EXTENSOR CARPI ULNARIS. Origin, from the middle third 

 of the posterior border of the ulna, from the common tendon 

 from the external condyle of the humerus, and from the fascia 

 of the forearm; insertion, into the base of the metacarpal bone 

 of the little finger, on the ulnar side; action, extends the wrist; 

 nerve, posterior interosseous. 



ANCONEUS. Origin, from the outer condyle of the hu- 

 merus ; insertion, into the upper fourth of the posterior aspect of 

 the shaft of the ulna and the side of the olecranon; action, 

 extends the forearm; nerve, musculo-spiral. 



Posterior Deep Layer. ^ 



SUPINATOR BREVIS. Origin, from the external lateral liga- 

 ment of the elbow- joint, from the external condyle of the hu- 

 merus, from the ulna below the lesser sigmoid cavity, and from 

 the orbicular ligament of the radius and the external lateral liga- 

 ment of the elbow-joint; insertion, into the neck, bicipital 

 tuberosity and oblique line of radius; the posterior interosseous 

 nerve pierces this muscle; action, supinates the hand; nerve, 

 posterior interosseous. 



