MOVEMENT OF THE LOWER END OF THE RADIUS. 109' 



and compares this line with the direction of the interosseous 

 fibres, it will be found that the two, while not quite parallel, 

 are nearly so. 



It results that each fibre of this part of the interosseous 

 membrane is not far from lying in the axis of circumduction 

 of the piece of the radius to which it is attached. Obviously 

 this arrangement is excellently suited for keeping the fibres 

 uniformly taut in every position, whether of pronation or 

 supination. 



The pull of the muscles which arise from the interosseous 

 membrane is transmitted chiefly to the radius. As the radius 

 alone articulates directly with the carpus, an equilibration of 

 forces round the wrist-joint will be established when these 

 muscles are in action. In this connection the direction of the 

 fibres of the interosseous membrane between tibia and fibula 

 deserves attention. Movements of pronation and supination do 

 not take place here, and the tibia is the sole column of support. 

 The fibres of the interosseous membrane run mainly downwards 

 from tibia to fibula. By this arrangement the strain of muscles 

 arising from the interosseous membrane and from the shaft of 

 the fibula is sent on to the tibia, and a balancing of forces 

 takes place round the ankle-joint similar to what occurs at the 

 wrist. Also the contraction of the group of muscles just 

 named will in no way interfere with the slight but important 

 movement of the fibula on the tibia which takes place in flexing 

 and extending the ankle-joint. 



