244 



POSTERIOR BRACHIAL REGION. 



Fig. 101. ception of the extensor carpi ulnaris. 



The muscle accompanies the exten- 

 sor ossis metacarpi. 



The EXTENSOR SECUNDI INTER- 

 NODII POLLICIS arises from the ulna, 

 and interosseous membrane. Its 

 tendon passes through a distinct 

 canal in the annular ligament, and 

 is inserted into the base of the last 

 phalanx of the thumb. 



Relations. By its external sur- 

 face with the same relations as the 

 extensor ossis metacarpi. By its 

 deep surface with the ulna, interos- 

 seous membrane, radius, wrist-joint, 

 radial artery, and metacarpal bone 

 of the thumb. The muscle is placed 

 between the extensor primi inter- 

 nodii and extensor indicis. 



The EXTENSOR INDICIS amesfrom 

 the ulna, as high up as the extensor 

 ossis metacarpi pollicis, and from 

 the interosseous membrane. Its 

 tendon passes through a distinct 1 

 groove in the radius, and is inserted 

 into the aponeurosis formed by the 

 common extensor tendon of the in- 

 dex finger. 



Relations. The same as those of 

 the preceding muscle, with the ex- 

 ception of the hand, where the ten- 

 don rests upon the metacarpal bone 

 of the fore-finger and second inter- 

 osseous muscle, and has no relation 

 with the radial artery. 



The tendons of the extensors, as 

 of the flexor muscles of the fore-arm, 

 are provided with synovial bursse 

 as they pass beneath the annular ligaments : those of the back of the 

 wrist have distinct sheaths, formed by the posterior annular ligament. 

 Actions. The anconeus is associated in its action with the triceps 



* The deep layer of muscles on the posterior aspect of the fore-arm. 1. The 

 lower part of the humerus. 2. The olecranon. 3. The ulna. 4. The anco- 

 neus muscle. 5. The supinator brevis muscle. 6. The extensor ossis meta- 

 carpi pollicis. 7. The extensor primi internodii pollicis. 8. The extensor 

 secundi internodii pollicis. 9. The extensor indicis. 10. The first dorsal inter- 

 osseous muscle. The other three dorsal interossei are seen between the meta- 

 carpal bones of their respective fingers. 



