(Chapter 12) Footnote 24:

Vesalius cites Book 9 of De usu partium, where see 3.718.14: “Perhaps someone may think that its length is greater than the diameter of the optic foramen, but if as a whole it is compared with the optic foramen as a whole, it will not appear any larger, or certainly not much larger.” Tr. May, op. cit. p. 442.