218 MUSCLES OF THE HAND. 



arm, are provided with synovial bursee as they pass beneath the . 

 annular ligaments: those of the back of the wrist have distinct 

 sheaths, formed by the posterior annular ligament. 



Actions. The anconeus is associated in its action with the tri- 

 ceps, extensor cubiti : it assists in extending the fore-arm upon the 

 arm. The supinator longus and brevis effect the supination of the 

 fore-arm, and antagonize the two pronators. The extensor carpi 

 radialis longior and brevior, and ulnaris, extend the wrist in opposi- 

 tion to the two flexors of the carpus. The extensor communis digi- 

 torum restores the fingers to the straight position, after being flexed 

 by the two flexors, sublimis and profundus. The extensor ossis 

 metacarpi, primi internodii, and secundi internodii pollicis, are the 

 especial extensors of the thumb, and serve to balance the actions of 

 the flexor ossis metacarpi, flexor brevis, and flexor longus pollicis. 

 The extensor indicis gives the character of extension to the index 

 finger, and is hence named " indicator," and the extensor minimi 

 digiti supplies that finger with the power of exercising a distinct 

 extension. 



MUSCLES OF THE HAND. 



Radial Region. 



Abductor pollicis, 

 Flexor ossis metacarpi (opponens), 

 Flexor brevis pollicis, 

 Adductor pollicis. 



Dissection. The hand is best dissected by making an incision 

 along the middle of the palm, from the wrist to the base of the fingers, 

 and crossing it at each extremity by a transverse incision, then 

 turning aside the flaps of integument. For exposing the muscles of 

 the radial region, the removal of the integument and fascia on the 

 radial side will be sufficient. 



The Abductor pollicis arises from the scaphoid bone and annular 

 ligament. It is inserted into the base of the first phalanx. 



Relations. By its superficial surface with the external portion of 

 the palmar fascia. By its deep surface with the flexor ossis meta- 

 carpi. On its inner side it is separated by a narrow cellular inter- 

 space from the flexor brevis pollicis. 



This muscle must be divided from its origin and turned upwards, 

 in order to see the next. 



The Flexor ossis metacarpi (opponens), arises from the trapezium 

 and annular ligament, and is inserted into the whole length of the 

 metacarpal bone. 



Relations. By its superficial surface with the abductor pollicis. 

 By its deep surface with the trapezio-metacarpal articulation and 

 with the metacarpal bone. Internally with the flexor brevis pollicis. 



The flexor ossis metacarpi may now be divided from its origin 

 and turned aside, in order to show the next muscle. 



