392 



MUSCLES AND FASCIAE. 



carpi Pollicis, and from the interosseous membrane. It terminates in a tendon . 

 which passes through a separate compartment in the annular ligament, lying 



in a narrow oblique groove at 

 Fig. 242.-Posterior Surface of the Forearm. Deep the back t of the lower end 



Muscles. f ,, v TJ. i-u 



of the radius. It then crosses 



obliquely the extensor tendons 

 of the carpus, being separated 

 from the other extensor ten- 

 dons of the thumb by a trian- 

 gular interval, in which the 

 radial artery is found ; and is 

 finally inserted into the base of 

 the last phalanx of the thumb. 



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 metacar- 

 pal bone of the thumb. 



The Extensor Indicis is a nar- 

 row 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 ori- 

 gin of the Extensor Secundi 

 Internodii Pollicis, and from 

 the interosseous membrane. Its 

 tendon passes with the Extensor 

 Communis Digitorum through 

 the same canal in the annular 

 ligament, and subsequently joins 

 that tendon of the Extensor 

 Communis which belongs to the 

 index finger, opposite the lower 

 end of the corresponding meta- 

 carpal bone. It is finally in- 

 serted into the second and third 

 phalanges of the index finger, in 

 the manner already described. 



Relations. They are similar to 

 those of the preceding muscles. 



Nerves. The Supinator Lon- 

 gus, Extensor Carpi Eadialis 

 Longior, and Anconeus, are 

 supplied by branches from the 

 musculo-spiral nerve. The re- 

 maining muscles of the radial 

 and posterior brachial regions, 

 by the posterior interosseous 

 nerve. 



Actions. The muscles of the 

 radial and posterior brachial 

 regions, which comprise all the extensor and supinator muscles, act upon the 

 forearm, wrist, and hand ; they are the direct antagonists of the pronator and 



CXTCNSOrt 

 CARPI ULNAKIS 



