146 THE NERVOUS SYSTEM 



tendons of the flexor digitorum profundus. They are inserted 

 into the radial side of the base of the proximal phalanx of each 

 of the medial four digits. In addition, their tendons are attached 

 to the expansion of the extensor tendons, which covers the 

 dorsal aspect of the proximal phalanx. By virtue of their 

 bony insertions, these muscles act as flexors of the metacarpo- 

 phalangeal joints, but by virtue of their connexion with the 

 extensor expansion they extend the two interphalangeal joints 

 at the same time (vide infra}. The lumbricals for the little 

 and ring fingers are supplied by the deep branch of the ulnar 



FIG. 66. Tendons attached to a Finger. (TURNER'S Anatomy.'] 



a. Kxtensor digitorum communis. 



b. Flexor digitorum profundus. 



c. Flexor digitorum sublimis. 



d. Lumbrical muscle. 



e. Dorsal interosseous muscle. 



f. Dorsal expansion of extensor tendon. 



nerve, but the lateral two lumbricals are innervated by the 

 median (p. 152). 



The Volar (Palmar] Interossei axe threfe in number, and they 

 act on the index, ring and little fingers. Each arises from the 

 volar aspect of the metacarpal bone of the finger on which it 

 acts, and each is inserted into the dorsum of the base of the 

 proximal phalanx and the extensor expansion. The volar 

 interossei for the ring and little fingers are inserted on the 

 radial sides of their respective phalanges, but that for the index 

 finger is inserted on the ulnar side. 



When the volar interossei contract, they adduct the index, 

 ring and little fingers to the middle finger. In addition, they 

 flex the metacarpo-phalangeal joints, while extending the inter- 

 phalangeal joints (cf. Lumbricals). 



