CHRISTIANIA VIDENSK.-SELSK. FORHANDL. 1 883. No. II. 47 



66. :,: Chr. Aeby, 



Beitrage zur Kenntniss der (ielenke. Deutsche Zeitschrift fur Chi- 

 rurgic 1876, VI Band, S. 354. 



67. * E F. 0. Ward, 



Human osteologi/. London 1876. Third edition. P. 221. 



263. It has occurred to me that the shape of the radius 

 is subject to a simple and constant mathematical law, which en- 

 ables us to express the relation of its extremities, by the following 

 general formula. The head of the radius is so disposed, in rela- 

 tion to the sigmoid cavity of the lower extremity, that the axis of 

 the former, if prolouged downwards, falls upon the centre of the 

 circle, of which the latter is a segment. This law, to which I have 

 not found a single exception, suggests a more precise definition of 

 the motions of the radius on the ulna, than has hitherto, I believe, 

 occurred to physiologists. Many authors have loosely stated, that 

 the radius rotates upon its own axis; an inexactitude into which 

 Sir Charles Bell, amongst other eminent physiologists, has fallen. 

 The inaccuracy of such a description may be rendered evident by 

 the following experiment. Let a recent fore-arm be fixed in a vice, 

 by the olecranon process, in such a manner as to leave the radius 

 its full freedom to rotation upon the ulna. Let a point be now 

 inserted into the centre of the cup-like cavity on the head of the 

 radius, and another into the centre of its inferior terminal surface, 

 so that the two points may coincide with the two extremities of 

 the long axis of the bone. The points being fixed, let it be at- 

 tempted to rotate the radius, or in anywise to change its relative 

 position with the ulna. This will be found impossible; the radius 

 being set fast, and incapable of any kind of motion. Cruveilhier 

 is clearly aware that the radius does not turn on its own axis 

 below; but he adopts the equally erroneous notion that the transverse 

 diameter of its lower extremity is the radius of the curve which 

 it describes around the ulna „le rayon de l'arc de cercle qu'il dé- 

 crit autour du cubitus" („Anatomie Descriptive", tom. I. p. 421). 

 On this supposition, the inner extremity of a line drawn across the 

 inferior surface of the radius, in the direction of its transverse 



