382 A MANUAL OF ANATOMY. 



Insertion. Into the outer surface of the olecranon, and 

 the upper fourth of the ulna. 



Nerve Supply. The musculospiral (through the seventh 

 and eighth cervical nerves). 



Action. To extend the forearm. 



Extensor Carpi Ulnaris. Fig. 78. 



Origin. From the external (epi) condyle of the humerus 

 by the common tendon, from the upper two-thirds of the 

 posterior ridge of the ulna in common with the flexor carpi 

 ulnaris and the flexor profundus digitorum, and from the 

 inner surface of the deep fascia of the forearm and the adja- 

 cent intermuscular septa. 



Insertion. Into the back of the base of the metacarpal 

 bone of the little finger. 



Nerve Supply. The posterior interosseous (the filaments 

 from the eight cervical). 



Action. To extend the wrist, to adduct the wrist, to 

 feebly extend the forearm. 



DISSECTION. 



Separate the superficial muscles from each other clear to their origins ; do 

 not remove the annular ligament yet until the deeper muscles have been studied, 

 after which it can be cut away as far as necessary to expose the relations of 

 the tendons to each other and to the back of the wrist. 



Trace the recurrent interosseous artery upward to the elbow, cutting through 

 the anconeus muscle. Follow downward from the supinator brevis, the pos- 

 terior interosseous artery and nerve, the former to its anastomosis with the 

 termination of the anterior interosseous, and the latter to the ganglion upon the 

 back of the wrist. 



Complete the cleaning of the radial artery and its branches, noting the 

 formation of the posterior carpal anastomoses. 



Remove the fascia from the interossei muscles and demonstrate their 

 insertion. 



Extensor Ossis Metacarpi Pollicis. Fig. 79. 



Origin. From the outer surface of the ulna for two 



