380 A MANUAL OF ANATOMY. 



other ; next is the extensor longus pollicis in a narrow 

 canal ; then in a broad one lies the tendons of the extensor 

 communis digitorum and the extensor indicis ; in a compart- 

 ment behind the radio-ulnar articulation is the slender ten- 

 don of the extensor minimi digiti, and lastly, lying in the 

 groove at the outer side of the styloid process of the ulna, 

 is the tendon of the extensor carpi ulnaris. 



Extensor Carpi Radialis Longior. Fig. 78. 



Origin. From the lower third of the external condyloid 

 ridge of the humerus and the intermuscular septa. 



Insertion. Into the radial side of the base of the second 

 metacarpal bone. 



Nerve Supply. The musculospiral (fibres from the sixth 

 cervical nerve). 



Action. Extend the wrist, feeble flexor of forearm, slight 

 abductor of wrist. 



Extensor Carpi Radialis Brevior. Fig. 78. 



Origin. By the common tendon from the external (epi) 

 condyle of the humerus, and from the intermuscular septa. 



Insertion. Into the radial side of the base of the third 

 metacarpal bone. 



Nerve Supply. The posterior interosseous branch of the 

 musculospiral. The fibres coming from the sixth and sev- 

 enth cervical nerves. 



Action. To extend the wrist, slight extensor of the fore- 

 arm. 



Extensor Communis Digitorum. Fig. 78. 



Origin. By the common tendon from the external (epi) 

 condyle of the humerus, and from the intermuscular septa, 

 and from the inner surface of the deep fascia of the forearm. 



Insertion. The muscle is provided with four tendons 

 which pass through the fourth compartment of the pos- 



