314 



MUSCLES AND FASCIA. 



Relations. By its superficial surface, with the same parts as the Extensor ossis 

 metacarpi pollicis. By its deep surface, with the ulna, interosseous membrane, 

 radius, the wrist, the radial vessels, and metacarpal bone of the thumb. 



The Extensor Indicis is a narrow elongated muscle, placed on the inner side of, 

 and parallel with, the preceding. It arises from the posterior surface of the shaft 



of the ulna, below the origin 

 Fig. 175. Posterior Surface of the Forearm. Deep Muscles. 



CARPI ULNARIS 



Extensor secundi inter- 

 nodii pollicis, and from the 

 interosseous membrane. Its 

 tendon passes with the Ex- 

 tensor comnmnis digitorum 

 through the same canal in the 

 annular ligament, and subse- 

 quently joins that tendon of 

 the Extensor communis which 

 belongs to the index-finger, 

 opposite the lower end of 

 the corresponding metacarpal 

 bone. It is finally inserted 

 into the second and third pha- 

 langes of the index-finger, in 

 the manner already described. 



Relations* They are simi- 

 lar to those of the preceding 

 muscles. 



Nerves. The Supinator lon- 

 gus, Extensor carpi radialis 

 longior, and Anconeus, are 

 supplied by branches from the 

 musculo-spiral nerve; the re- 

 maining muscles of the ra- 

 dial and posterior brachial 

 regions, by the posterior inter- 

 osseous nerve. 



Actions. The muscles of 

 the radial and posterior bra- 

 chial regions, which comprise 

 all the Extensor and Supinator 

 muscles, act upon the fore- 

 arm, wrist, and hand; they 

 are the direct antagonists of 

 the Pronator and Flexor 

 muscles. The Anconeus as- 

 sists the Triceps in extending 

 the forearm. The Supinator 

 longus and brevis are the 

 supinators of the forearm and 

 hand ; the former muscle more 

 especially acting as a supina- 

 tor when the limb is pronated. 

 When supination has been 

 produced, the Supinator lon- 

 gus, if still continuing to act, 

 flexes the forearm. The Ex- 

 tensor carpi radialis longior 

 and brevior, and Extensor 

 carpi ulnaris muscles, are the 



