MUSCLES OF THE HAND. 245 



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 lon- 

 gior and brevior, and ulnaris, extend the wrist in opposition to the 

 two flexors of the carpus. The extensor communis digitorum re- 

 stores 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 meta- 

 carpi, flexor brevis, and flexor longus pollicis. The extensor indicis gives 

 the character of extension to the index finger, arid 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 or Thenar 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 turn- 

 ing 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 is a small, thin muscle, which arises from 

 the scaphoid bone and annular ligament. It is inserted into the base 

 of the first phalanx of the thumb. 



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 pollicis) 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 shew the next muscle. 



The FLEXOR BREVIS POLLICIS consists of two portions, between 

 which lies the tendon of the flexor longus pollicis. The external portion 



