6l2 



HUMAN ANATOMY. 



I. Interossei Volares (Fig. 589). 



Attachments. — The volar or palmar interossei are four slender muscles 

 situated in the intervals between the metacarpal bones and resting upon the in- 

 terossei dorsales. ^\iQ first and second muscles, counting from the radial side, arise 

 from the ulnar side of the bases of the first and second metacarpals, and are inserted 

 into the ulnar side of the base of the first phalanx and, in the case of the second 

 muscle, also into the membranous expansion of the long extensor tendon of the 



Fig. 590. 



Extensor carpi ulnaris 

 tendon 



Extensor carpi radialis longior tendon 



Extensor carpi radialis brevior 

 tendon 



Extensor longus pollicis 

 \J^^ tendon 



Second dorsal interosseus 



Third dorsal interosseus 

 Fourth dorsal interosseus 



Extensor communis 

 digitorum tendons 



Dissection of back of hand, showing dorsal interossei and insertion of extensor tendons. 



corresponding digit. The third zxiAfoiirth muscles arise from the radial side of the 

 fourth and fifth metacarpals, and are inserted similarly to the second muscle, but 

 into the radial sides of the fourth and fifth digits. 



Only three palmar interossei are usually described by English anatomists, the muscle in- 

 cluded in the series by the German school as the first interosseus {m. interosseus primus volaris) 

 being regarded as the small ulnar head of the flexor brevis pollicis (page 608). The inclusion 

 of this muscle in the series of palmar interossei is warranted by its morphological relations. 



Nerve-Supply. — By the deep division of the ulnar nerve from the eighth 

 cervical and first thoracic nerves. 



Action. — To draw the first, second, fourth, and fifth digits towards the middle 

 finger and to flex the first phalanx of the same digits. 



