154 MUSCLE TISSUE 



of the anterior surface of the ulna for the lower fourth, 

 and from the inferior from the radiocarpal joint; 

 inserted into the anterior surface and anterior margin 

 of the shaft of the radius for a little less than its fourth. 



The Radial Region. Three in number, from the lower 

 third of the arm and upper third of the forearm in an 

 almost continuous row. 



Supinator longus rises from the upper two-thirds 

 of the external supracondylar ridge of the humerus 

 and external intermuscular septum, limited above by 

 the spiral groove; thin fleshy belly ends at the middle 

 of the forearm in a flat tendon which expands at its 

 insertion into the outer side of the radius at the base 

 of the styloid process. 



Extensor carpi radialis longior arises from the lower 

 third of the external supracondylar ridge and external 

 intermuscular septum and a few fibers from the com- 

 mon tendon ; inserted into the radial half of the posterior 

 surface of the base of the second metacarpal. 



Extensor Carpi Radialis Brevior. Origin, by the 

 common extensor tendon from the outer condyle, 

 septa, external lateral ligament, fascia, and a fibrous 

 arch over the radial nerve and radial recurrent vessels ; 

 insertion, into the radial half of the posterior surface of 

 the base of the metacarpal bone of the middle finger. 



The Posterior Radioulnar Region. SUPERFICIAL 

 LAYER. Extensor Communis Digitorum. Origin, com- 

 mon extensor tendon from the external condyle of the 

 humerus, orbicular ligament, fascia, and septa; there 

 are three fleshy bellies, the innermost divided into two, 

 four passing under the posterior annular ligament; 

 the first and second pass to the index and middle 

 fingers connected by a weak band, always transverse; 

 the first is joined by the extensor indicis tendon at 

 the metacarpophalangeal joint; the third runs to the 

 ring finger and sends a slip to the middle finger tendon; 

 the fourth divides, the outer larger part going to the 

 ring finger, the inner part joining the outer division 



