210 MYOLOdY, OR ANATOMY OF MUSCULAR SYSTEM 



have separate twigs; the flexor longus pollicis, pronator quad- 

 ratus, and outer half of the flexor profundus by the anterior 

 interosseous branch of the median. Flexor carpi ulnaris and 

 inner half of the flexor profundus by the ulnar. 



The Radial Region 



Three in number, from the lower third of the arm and upper 

 third of the forearm in an almost continuous row. 



1. M. supinator longus (brachioradialis) 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; its inner edge is united by fascia to the flexor carpi 

 radialis; it sends some fibers to the aponeurosis on the back 

 of the forearm. 



2. M. extensor carpi radialis longior rises from the lower 

 third of the external supracondylar ridge and external inter- 

 muscular septum and a few fibers from the common tendon; 

 inserted into the radial half of the dorsal surface of the base 

 of the second metacarpal. 



3. M. Extensor Carpi Radialis Brcvior. 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 dorsal surface of the base of the metacarpal bone 

 of the middle finger. 



These tendons are crossed by the tendons of the first two 

 thumb extensors a little above the wrist. 



The Posterior Radioulnar Region 



Two layers, muscles of the superficial layer inserted into 

 the ulnar edge of the forearm and hand and into the fingers 

 from the fifth to the second inclusive; of the deep layer into 

 the radial edge of the forearm and hand and two outer fingers. 



SUPERFICIAL LAYER. 1. M. Extensor Communis Digitorum. 

 Origin (from neither ulna nor radius), common extensor 

 tendon from the external condyle of the humerus, orbicular 



