(Chapter 27) Footnote 16:

Radialis / ulnaris. In the standard anatomical ventral view, the palms of the hands face forward; Vesalius’ “outside” of the thumb becomes in modern terminology the “radial side,” the “inside” of the thumb is termed “ulnar side”; the “outside” of the index finger (thumb side) is the “radial” side, the “inside” the “ulnar” (or little finger) side, etc. This is, of course, very confusing to the reader since the “outside” of the hand means the dorsal side and the “inside” means palmar.