EXTENSOR COMMUNIS DIGITORUM, 



235 



Fig. 124 * 



its deep surface with the brachialis anticus, extensor carpi radialis longior, 

 tendon of the biceps, supinator brevis, pronator radii teres, flexor carpi 

 radialis, flexor sublimis digitorum, flexor longus pollicis, pronator quad- 

 ratus, radius, musculo-spiral nerve, radial and posterior interosseous nerve, 

 and radial artery and veins. 



This muscle must be divided through the middle, and the two ends 

 turned to either side to expose the next muscle. 



The EXTENSOR CARPI RADIALIS LONGIOR arises 

 from the external condyloid ridge below the pre- 

 ceding, and from the intermuscular fascia. Its ten- 

 don passes through a groove in the radius, imme- 

 diately behind the styloid process, to be inserted 

 into the base of the metacarpal bone of the index 

 finger. 



Relations. By its superficial surface, with the 

 supinator longus, extensor ossis metacarpi pollicis, 

 extensor primi internodii pollicis, extensor secundi 

 internodii pollicis, radial nerve, fascia of the fore- 

 arm, and posterior annular ligament. By its deep 

 surface, with the brachialis anticus, extensor carpi 

 radialis brevior, radius and wrist joint. 



The EXTENSOR CARPI RADIALIS BREVIOR is seen 

 by drawing aside the former muscle. It arises from 

 the external condyle of the humerus and intermus- 

 cular fascia, and is inserted into the base of the me- 

 tacarpal bone of the middle finger. Its tendon is 

 lodged in the same groove, on the radius, with the 

 extensor carpi radialis longior. 



Relations. By its superficial surface, with the 

 extensor carpi radialis longior, extensor ossis meta- 

 carpi pollicis, extensor primi internodii pollicis, ex- 

 tensor secundi internodii pollicis, fascia of the fore- 

 arm, and posterior annular ligament. By its deep 

 surface, with the supinator brevis, tendon of the 

 pronator radii teres, radius and wrist joint. By its 

 ulnar bonier, with the extensor communis digitorum. 



The EXTENSOR COMMUNIS DIGITORUM arises from the external condyle, 

 and intermuscular fascia ; and divides into four tendons, which reinserted 

 into the second and third phalanges of the fingers. At the metacarpo- 

 phalangeal articulation, each tendon becomes narrow and thick, and sends 

 a thin fasciculus upon each side of the joint. It then spreads out, and 

 receiving the tendon of the lumbricalis, and some tendinous fasciculi from 



* The superficial layer of muscles of the posterior aspect of the fore-arm. 1. Tha 

 lower part of the biceps. 2. Part of the brachialis anticus. 3. The lower part of the 

 triceps, inserted into the olecranon. 4. The supinator longus. 5. The extensor carpi 

 radialis longior. 6. The extensor carpi radialis brevior. 7. The tendons of insertion 

 of these two muscles. 8. The extensor communis digitorum. 9. The extensor minimi 

 digiti. 10. The extensor carpi ulnaris. 11. The anconeus. 12. Part of the flexor carpi 

 ulnaris. 13. The extensor ossis metacarpi and extensor primi internodii muscle, lying 

 together. 14. The extensor secundi internodii; its tendon is seen crossing the two ten- 

 dons of the extensor carpi radialis longior and brevior. 15. The posterior annular liga- 

 ment. The tendons of the common extensor are seen upon the back of the hand, and 

 their mode of distribution o the dor sum of the ringers. 



