THE HAND. 



second, is inserted the extensor carpi radialis longior; into the base of the third (and 

 part of the second) is inserted the extensor carpi radialis brevior, and into the base of 

 the fifth, the extensor carpi ulnaris (Fig. 361). 



Thus it will be seen that all the flexors and extensors of the wrist have their 

 ultimate insertion into the metacarpal bones. 



The metacarpal bone of the thumb has inserting into its base the extensor ossis 

 metacarpi pollicis tendon. As this tendon has its origin in the forearm it also acts as 



Flexor profundus digitorum 



Flexor sublimis 

 digitorum 



FIG. 362. Palmar view of the flexor tendons of the finger, showing the insertion of the flexor sublimis into the 

 middle phalanx and the flexor profundus into the distal phalanx. 



a carpal extensor, but owing to the movability of the thumb it acts especially as an 

 extensor of the latter, the carpus remaining immovable. 



The Phalanges. The thumb has two phalanges and the fingers each three. 

 These are called the proximal, middle, and distal phalanges, also the first, second, 

 and third phalanges. The thumb has only a proximal and a distal phalanx. 



Extensor communis digitorum 



Interosseous m 

 Lumbricalis m 



uscl 



Extensor aponeurosis 

 FIG. 363. Lateral view of the extensor tendons of the finger. 



Into the middle phalanges on their palmar surfaces are inserted the flexor sub- 

 limis digitorum tendons and into the distal the flexor profundus (Fig. 362). 

 There is only one long flexor to the thumb and it is inserted into the distal phalanx. 



The extensor communis digitorum opposite the metacarpophalangeal joints 

 sends off a fibrous expansion which blends with the lateral ligaments of the joints 



Extensor aponeurosis 



Extensor communis 

 digitorum 





Interosseous 

 muscle 

 Lumbricalis muscle 



FIG. 364. Dorsal view of the extensor tendons of the finger. 



(Fig. 363). On the dorsum of the proximal phalanx the tendon splits into three 

 parts. The middle slip inserts into the bases of the middle phalanges, while the two 

 lateral slips, after receiving the insertions of the lumbricales and part of the insertions 

 of the interossei, insert into the bases of the distal phalanges of the fingers (Fig. 364). 

 The thumb has two separate extensors, the extensor brevis pollicis and the extensor 

 longus pollicis. 



Into the bases of the proximal phalanges are inserted the remaining portion of 

 the tendons of the interossei muscles, which move the fingers toward and from one 

 another, and slips from the palmar fascia. The main function of the interossei and 



