180 THE UPPER EXTREMITIES. 



in cases of fracture their relative position is of consid- 

 erable importance as showing the amount of deformity. 



The two forearm bones are more frequently broken 

 together than separately and generally by direct vio- 

 lence, the lower fragment being usually drawn up by 

 the action of the flexor and extensor muscles and pro- 

 ducing a swelling on the palmar surface of the forearm. 

 Indirect violence usually causes fracture of the radius 

 only. In both cases, but especially in fracture of both 

 bones, there is a tendency for membrane to get between 

 the fragments, so the arm is put up in splints with the 

 hand midway between pronation and supination in 

 order to separate the bones as far as possible. Care 

 must be taken not to have the bandage too tight or gan- 

 grene of the fingers may result. In most fractures of 

 the arm it is put up bent, but in fracture of the olecranon 

 it is put up fully extended, as the fragment is sure 

 otherwise to be displaced by the pull of the triceps. In 

 fact, the olecranon is sometimes fractured by the mus- 

 cular force of the triceps, though usually its fracture, 

 which is frequent, is due to direct violence. The ulna 

 is also often fractured in the middle by direct violence 

 or the styloid process may be broken. Fracture of the 

 neck or shaft of the radius is very common, the most 

 important arm fracture being that of the lower end 

 of the radius or Colles' fracture. This and the corre- 

 sponding fracture in the leg, Pott's fracture, are two of 

 the commonest fractures. In dislocation of the wrist 

 the normal relation of the two styloid processes remains 

 unchanged, but in Colles' fracture the lower fragment 

 often projects on the back of the hand, making a typical 

 deformity called the silver fork deformity. 



The bones of the wrist and hand had best be de- 

 scribed before the forearm muscles are taken up, as the 

 muscles of the forearm are distributed largely to the 

 fingers. 



The Wrist. The wrist or carpus is made up of eight 

 bones arranged in two rows of four each. In the first 



