(Chapter 14) Footnote 2:

Neither LSJ nor Durling 1993 give “spine” as a meaning for nw=ton, which is the general term for the back. Only in its adjectival form nwtiai=oj, “spinal,” does the root refer to the bone. The 1555 edition moves the Greek nomenclature to the first sentence of the main text, providing as its introduction to the figure legend an abbreviated version of this sentence and deleting the second sentence entirely.