392 



THE MUSCULAE SYSTEM. 



thumb which produce the thenar eminence, the three muscles of the little finger, 

 which form the hypothenar eminence, and the interossei muscles, which are 

 deeply placed between the metacarpal bones. 



Muscles of the Thumb. 



The short muscles of the thumb are the abductor, opponens, and flexor brevis 

 (with its deep portion, interosseus primus volaris), and the adductor muscle, sub- 

 divided into two heads oblique and transverse. 



M. Abductor Pollicis Brevis. The abductor pollicis brevis (O.T. abductor 

 pollicis) arises by fleshy fibres from the tubercle of the navicular, the ridge of the 

 greater multangular, the volar surface of the transverse carpal ligament, and from 



Capitate bone 



Navicular bone 

 Abductor pollicis brevis (origin) 



Opponens pollicis (origin) 



Greater multangular bone 

 Abductor pollicis longus 

 (insertion) 



Lesser multangular bone 

 Opponens pollicis (insertion) 



Flexor carpi radialis 

 (insertion) 



Adductor pollicis 

 (origin of oblique 

 9 head) 



First dorsal interosseous muscle 

 (one origin) 



First volar interosseous muscle 

 (origin) 



Second dorsal interosseous 

 muscle (one origin) 



Os lunatum 



Os hamatum 



Os triquetrum 

 Pisiform bone 



Abductor digiti quinti (origin) 



Flexor carpi ulnaris (insertion) 



Flexor brevis digiti quinti 

 (origin) 



Flexor carpi ulnaris (insertion) 



Opponens digiti quinti 

 (origin and insertion) 



Third volar inter- 

 osseous muscle 

 (origin) 



Fourth dorsal interosseous 

 muscle (one origin) 



Second volar interosseous 



muscle (origin) 



Adductor pollicis (origin 

 of transverse head) 



Third dorsal interosseous 

 muscle (one origin) 



FIG. 351. MUSCLE-ATTACHMENTS TO THE VOLAR ASPECT OF THE CARPUS AND METACARPUS. 



tendinous slips derived from the insertions of the palmaris longus and abductor 

 pollicis longus muscles (Fig. 350, p. 391). Strap-like in form, and superficial in 

 position, it is inserted by a short tendon into the radial side of the first phalanx of 

 the thumb at its proximal end, and into the capsule of the metacarpo-phalangeal 

 joint. 



Nerve-Supply. Median nerve (C. 6. 7.). 



Actions. The muscle acts on the thumb at both the carpo-metacarpal and metacarpo- 

 phalangeal joints. It abducts and draws forward the thumb. 



M. Opponens Pollicis. The opponens pollicis arises by fleshy and tendinous 

 fibres from the volar surface of the transverse carpal ligament and from the ridge 

 on the greater multangular bone. It is partially concealed by the preceding 

 muscle. 



Extending distally and laterally it is inserted into the whole length of the 

 lateral border and the radial half of the volar surface of the first metacarpal bone i 

 (Fig. 351, p. 392). 



