104 



DK JAMES F. GEMMILL. 



manner described above. points to the centre of the head 

 of the uhia, which corresponds almost exactly to the centre of 

 curvature of C.C. L and S point respectively to the place of 

 insertion of the triangular ligament and to the tip of the styloid 

 process of the ulna. M represents the position of the needle 

 fixed in the radius at semi-pronation, and M' and M" the 

 position of the needle in pronation and supination respectively. 



'^fl 



Fig. 1. — C.C, circumduction curve ; 0, centre of head of ulna ; L, attachment 

 of triangular ligament ; S, tip of styloid process of ulna. (Explanation in 

 text. ) 



Circles (the dotted ones) have been described with L.M. and 

 S.M. as radius ; and it will be seen that these circles by 

 no means coincide with the circumduction curve. Also the 

 distances S.M.' and S.M." are less than the distance S.M. — that 

 is to say, the distance between the styloid processes of radius and 

 ulna is less in full pronation and supination than in the middle 

 position. This fact can be verified on the living subject. 

 Accurate measurement is, perhaps, impossible, but by means of 

 a suitable pair of callipers or by a clamp, approximate results 



