

UPPER EXTREMITY AND THORAX, POSTERIOR. 381 



terior annular ligament in a bunch. Lower down they 

 separate to pass to their respective fingers. Across the 

 knuckles the tendons of the three outer fingers are united 

 by fibrous bands which diverge from the tendon of the ring 

 finger to the tendons of the middle and little finger on 

 either side. The insertion into the fingers is as follows : 



From the side of each tendon a fibrous extension passes 

 to the lateral ligaments of the metacarpophalangeal articu- 

 lations. Beyond this each tendon divides into three slips. 

 The middle slip is inserted into the base of the second 

 phalanx, the two lateral slips pass forward to be inserted 

 into the base of the last phalanx. 



Each tendon of the extensor communis digitorum re- 

 ceives laterally the insertions of the lumbricales (see page 

 307) and the dorsal and palmar interossei muscles (palmar, 

 see page 309 ; dorsal, page 388). 



Nerve Supply. The posterior interosseous (the filaments 

 issue from the seventh cervical nerve). 



Action. To extend the fingers, hand, and wrist, to 

 slightly extend the forearm. 



Extensor Minimi Digiti. Fig. 78. 



Origin. The same as the preceding, with which it 

 unites for the upper third of its length. 



Insertion. Into the tendon of the common extensor 

 going to the little finger. 



Nerve Supply. Same as the preceding. 



Action. To extend the little finger, the hand, and the 

 wrist, and a very feeble extensor of the elbow. 



Anconeus. Fig. 78. 



Origin. From the back of the external (epi) condyle of 

 the humerus, and from the posterior ligament of the elbow- 

 joint. 



