484 



THE MUSCLES AND FASCIA. 



FIG. 308. Posterior surface of the forearm. 

 flcial muscles. 



Super- 



musculo-spiral groove. The fibres 

 terminate above the middle of the fore- 

 arm in a flat tendon which is inserted 

 into the outer side of the base of 

 the styloid process of the radius. 



Relations. By its superficial sur- 

 face, with the integument and fascia 

 for the greater part of its extent ; 

 near its insertion it is crossed by the 

 Extensor ossis metacarpi pollicis and 

 the Extensor brevis pollicis ; by its 

 deep surface, with the humerus, the 

 Extensor ' carpi radialis longior and 

 brevior, the insertion of the Pronator 

 radii teres, and the Supinator brevis; 

 bv its inner border, above the elbow, 

 w'ith the Brachialis anticus, the 

 musculo-spiral nerve, and radial re- 

 current artery ; and in the forearm 

 with the radial vessels and nerve. 



The Extensor carpi radialis longior 

 is placed partly beneath the pre- 

 ceding muscle. It arises from the 

 lower third of the external condyloid 

 ridge of the humerus, and from the 

 external intermuscular septum. The 

 fibres terminate at the upper third of 

 the forearm in a flat tendon, which 

 runs along the outer border of the 

 radius, beneath the extensor tendons 

 of the thumb ; it then passes through 

 a groove common to it and the Ex- 

 tensor carpi radialis brevior, imme- 

 diately behind the styloid process, and 

 is inserted into the base of the meta- 

 carpal bone of the index finger, on its 

 radial side. 



Relations. By its superficial sur- 

 face, with the Supinator longus, and 

 fascia of the forearm; its outer side-is 

 crossed obliquely by the extensor ten- 

 dons of the thumb ; by its deep surface, 

 with the elbow-joint, the Extensor 

 carpi radialis brevior, and back part 

 of the wrist. 



The Extensor carpi radialis brevior 

 is shorter, as its name implies, and 

 thicker than the preceding muscle, be- 

 neath which it is placed. It arises 

 from the external condyle of the 

 humerus by a tendon common to it 

 and the three following muscles ; from 

 the external lateral ligament of the 

 elbow-joint, from a strong aponeurosis 

 which covers its surface, and from 

 the intermuscular septa between it and 

 the adjacent muscles. The fibres ter- 



