CHRISTIANIA VIDENSK.-SELSK. FORHANDL. 1883. No. II. 31 



42. E G. M. Humphry, 

 Human Skeie ton. Cambridge 1S~>8. P- 377. 



The bones of the fore-arm present råtner more interest than 

 attaches to the other long bones, because, in addition to their move- 

 ment together upon the humerus, the radius undergoes a partial 

 revolution upon the ulna for the purpose of permitting the prona- 

 tion and supination of the hand. In this movement the radius 

 ro tåtes upon an axis drawn straight downwards, as a plumb-line 

 would fall, through the most prominent part of the articular surface 

 of the outer condyle of the humerus. The upper portion of this axis pas- 

 ses directly trough the centre of the button-like head of the radius, 

 which rests upon the condyle. But as we trace it lower down, in conse- 

 quence of the inclination of the bones of the fore-arm outwards from the 

 humerus at the elbow, it soon ceases to traverse the radius, and 

 take its course, along the interosseous space, to the lower end of 

 the ulna, through the middle of which it runs, just as above it had 

 run through the middle of the end of the radius. Accordingly, 

 in pronation and supination, the upper articular surface of the 

 radius ro tåtes upon its own axis, on the tubercle of the humerus, 

 and in the lesser sigmoid cavity of the ulna: wheras the lower end 

 of the radius plays around the lower extremity of the ulna, and 

 describes a segment of a circle upon it, revolving upon an axis 

 which passes through the centre of the extremity of that bone. 

 Thus, although the axes of movement of the two extremities of the 

 radius in pronation and supination coincide in the same perpen- 

 dicular line; that of the one passes through the end of the radius, 

 and that of the other through the end of the ulna '. If now this 

 perpendicular line be prolonged downwards through the hand it 

 passes through the ring finger; so that, in the movement referred 

 to, the hand, with the radius, rotates upon an axis drown from the 

 middle of the outer tubercle of the humerus to the extremity of 

 the ring finger; and the axis traverses the lower end of the ulna. 



I find that Mr. Ward (in his Human Osteology, p. 312) describes correctly this 

 asie of rotation of the radius, and illustr;.tes it by a diagram. 



