MOVEMENT OF THE LOWER END OF THE RADIUS. 



105 



may be got. I was able to make out an appreciable narrowing 

 in transverse measurement in each one of a considerable number 

 of wrists experimented on. 



Attention does not seem to have been called to the fact, that 

 in the course of circumduction the lower end of the radius 

 changes its level relatively to the lower end of the ulna. A 

 certain amount of vertical motion on the part of any point in 

 the lower end of the radius relatively to the ulna is involved in 

 circumduction. 



Disarticulate a forearm at the wrist joint. Fix the ulna 

 immovably perpendicular to a fixed plane in such a manner 

 that the styloid process of the radius is just touching the plane 

 when in the semi-prone position. If pronation and supination 

 be now carried out, it will be found that in both of these posi- 



FiG. 2. — R and U, radius and ulna near semi-pronation ; A, axis of circumduc- 

 tion cone. The dotted outline R' the radius near extreme pronation. 

 The level of the lower end of R is indicated by the horizontal line L, and 

 that of R' by the line L'. The distance (D) between L and L' represents 

 the amount of vertical motion relatively to the ulna of the styloid process 

 of the radius in pronation. 



tions, but especially in full pronation, the styloid process of the 

 radius recedes considerably from the fixed plane. In well- 

 developed forearms this recession of the styloid process amounts 

 to as much as 2- or 3-sixteenths of an inch. All points in the 

 distal end and shaft of the radius, lower than the place of 

 emergence from the radius of the axis of circumduction, undergo 

 a vertical movement similar in kind, but less in amount, accord- 

 ing as the points taken are nearer the inner border or higher up 



