(Chapter 14) Footnote 24:

Vesalius adds this qualification because his source (still Galen, De usu partium 4.60.2) wrongly gives the number of nerves as 58 (29 pairs) and Vesalius assumes he is thinking of an animal’s spine. As when correcting Galen on the bones of the sacrum (see note 5 above), he does not openly call attention to Galen’s error.