134 



THE UPPER EXTREMITY 



distal third of the lateral epicondylar ridge of the humerus, 

 and from the lateral intermiisciilar septum. From the fleshy 

 portion of the muscle a long tendon proceeds, which passes 

 under cover of the dorsal carpal ligament, and is inserted 

 into the dorsal aspect of the base of the metacarpal bone of 

 the index finger. This muscle is supplied by the radial nerve 

 ( musculo- spiral). 



M. Extensor Carpi Radialis Brevis (O.T. Extensor Carpi 



Os triquetrum 

 Os pisiform 



Os hamatum 



Extensor carpi ulnari 



Os lunatum 



Os capitatum 



Os naviculare manus 

 Extensor carpi radialis brevis 

 ,Os multangulum minus 

 k/ Os multangulum majus 



Extensor carpi radialis longus 

 Abductor pollicis longus 



FIG. 52. Dorsal aspect of the Bones of the Carpus and Metacarpus 

 with Muscular Attachments mapped out. 



Radialis Brevior). The extensor carpi radialis brevis is 

 closely associated with the preceding muscle. It arises by 

 the common extensor tendon from the lateral epicondyle of 

 the humerus ; it also derives fibres from the radial collateral 

 ligament of the elbow-joint, from the investing deep fascia, 

 and the fibrous septa in connection with it. The tendon 

 of the muscle accompanies that of the long radial extensor 

 under cover of the dorsal carpal ligament, and is inserted 

 into the dorsal aspect of the base of the third metacarpal 

 bone immediately beyond the root of its styloid process. 

 This muscle is supplied by the dorsal interosseous nerve. 



