146 ANATOMY OF UPPER EXTREMITY, ETC. 



DISSECTION Till. 



BACK OF THE FOREARM AND HAND. 



The skin is to be removed from the back of the arm and hand. 

 The muscles are covered in by a dense fascia continuous with that of 

 the front of the arm ; this may be removed at its lower part, but it is 

 adherent to the bellies of the muscles above ; the muscles should be 

 separated by tracing them upward from their tendons. The back of 

 the arm is more difficult to dissect neatly than the front. 



Before commencing the dissection of the muscles, the 

 dorsal branch of the radial nerve should be followed out. 

 It becomes cutaneous at the lower third of the radius, and 

 divides into two branches ; one of which is distributed to 

 the radial border and ball of the thumb ; the other divides 

 into dorsal digital branches and supplies the remaining 

 side of the thumb, both sides of the next two fingers, and 

 half the ring finger. The dorsal branch of the ulnar nerve, 

 appearing near the styloid process of the ulna, supplies 

 both sides of the little finger, and the contiguous side of 

 the ring finger upon their dorsal surfaces. 



The muscles of the back of the arm are divided into two 

 layers ; the separation is not well defined, and the muscles 

 are not so voluminous as those of the front of the arm. 



The EXTENSOR CARPI RADIALIS LONGIOR lies upon the 

 radial side of the arm, just below the supinator longus, by 

 which it is partly covered ; it arises from the external 

 condyloid ridge of the humerus, and its tendon passes 

 through a well-marked groove in the head of the radius, 

 which is covered by the posterior annular ligament, to be 

 inserted into the base of the metacarpal bone of the index 

 finger. The radial nerve lies along the outer border of its 

 tendon. 



The EXTENSOR CARPI RADIALIS BREVIOR immediately 

 succeeds the preceding muscle, and is partly covered by 

 it ; it arises from the outer condyle of the humerus, and 

 the tendon common to the extensor muscles ; it forms a 

 tendon closely united with that of the extensor carpi radi- 

 alis longior, and passes through the same groove in the 

 radius, beneath the annular ligament ; after which it di- 

 verges from it, and is inserted into the base of the meta- 

 carpal bone of the middle finger. The tendons of both 

 these muscles pass beneath the extensor tendons of the 

 thumb. 



