(Chapter 25) Footnote 27:

Vesalius’ point is that the styloid process of the ulna is not articular as Galen had stated in De usu partium 3.133 and elsewhere (see Ch. 24, n. 54), but functions only as a structure corresponding to the styloid process of the radius, helping to contain the wrist bones within the articular capsule formed by the radius and ulna.