Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 24 On the Bones of the Forearm: the Ulna and Radius

Account of the lower part of the radius

On the surface of the radius (all of figs. 7 and 8) adjacent to the wrist, which we have said widens and thickens, several things call for exact scrutiny. First, this part had to be enlarged to establish a satisfactory surface for the articulation of the carpus (1, 2, 3 in the first five figs. of ch. 25); 51 for it was necessary that the joint of the wrist with the forearm in humans be assigned a little less than completely on the radius 52 if when the ulna is stationary with respect to the humerus the hand was to be pronated and supinatedwith the benefit and aid of the radius. If equal portions were carved in the depressions of the radius and ulna to which the carpus is articulated, and the resulting articular cavity that matches the upper surface of the carpus had as the inevitable result to be transversely oblong, it would obviously have been impossible for both the radius and the hand to be pronated and supinated when the ulna was stationary on the humerus and performing as if it were the base and fulcrum of this motion. The part of the carpus which is inserted or articulated into the depression of the ulna would be in the way like a nail, preventing the radius from moving at all if the ulna did not move. For this reason it was worthwhile to thicken the lower part of the radius so that it would be suitable to make a socket to which the carpus could be articulated. But since it was not expedient to thicken a thin bone too much, Nature wished also that a portion be supported by the ulna, but in such a way that the ulna make contact with the carpus at scarcely more than a point. This contact is made by a sharp process [p. styloideus] (R in figs. 1, 2) which anatomists liken to a stylus.



Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 24 On the Bones of the Forearm: the Ulna and Radius