102 DR JAMES F. GEMMILL. 



centre of the circumduction curve. In this respect he is 

 followed by Holden}- Morris {loc. cit.) and Brimton in Todd's 

 Cydo'pccdia {loc. cit.) ; but while, according to Ward, this point 

 lies in the middle of the head of the ulna, according to the 

 other two it is placed in the groove between the styloid process 

 and head of the ulna. 



In the other works which I have been able to consult, the 

 centre of the circumduction curve is placed more or less defi- 

 nitely in the centre of the head of the ulna. Thus Sappcy- 

 states that the inferior extremity of the radius turns round the 

 axis of the ulna. So also KrauseJ The same idea is implied, if 

 not expressly stated, in a paper by Hciherg.'^ According to 

 Mayer, ^ the axis of circumduction of the radius " passes through 

 the capitulum ulna; rather nearer the styloid process of the 

 ulna." By Tcstut^ the axis of circumduction is said to "pass 

 through the head of the ulna." Macalister '' states that the axis 

 of motion traverses the lower end of the ulna external to the 

 styloid process, and Gray^ that rotation takes place round an 

 axis which corresponds to the centre of the head of the ulna. 



The view given by Ward, Macalister, Gray, and the others 

 last quoted is, I think, the right one ; but as it differs from the 

 account given by so many others, the whole matter may be said 

 to be still open for discussion and analysis. The point at issue, 

 be it stated here, is independent of the vexed question regarding 

 movement of the ulna in pronation and supination. Movement 

 of the radius alone, in relation to the head of the ulna, falls to 

 be considered here. 



The chief factor determining the form of the circumduction 

 curve is to be found, not, as indicated by Ward {loc. cit.), in the 

 curvature of the lesser sigmoid cavity, but in the curvature of 

 the articular surface of the ulna at the inferior radio-ulnar 

 joint. This curvature in the plane of circumduction is a segment 



^ Human Osteology, 1887, p. 316. 



- Anatomie Descriptive, 1867, torn. i. p. 622. 



^ Speclelle und MahvscojnscJic Anatomic, 1879, vol. ii. \\ 101. 



■^ Journal of Anatomy and Pliysiology, vol. xix. p. 239. 



^ Statik u. Mechanik des Menschlichen Knoclien-geriistes, 1873, p. 142-143. 



'' Traitd d'Anafinin'/' Ilumaine, vol. i. p. 401. 



'■ Human Anatomy, 1889, p. 154. 



** Human Anatomy, 1897, p. 350. 



