(Chapter 15) Footnote 41:

This and the preceding sentence were rewritten as follows in the 1555 edition: “Its body is somewhat hollowed on its posterior surface where the dorsal medulla enters so that a prominent process of the second vertebra, which we shall call the dens, may be placed in the body of the first vertebra like a kind of axle; this vertebra (as we shall later explain more fully) is turned upon it together with the head. That this may more readily happen, the anterior surface of the area hollowed out in the body of the first vertebra has a lightly hollowed depression (L in figs 3 and 4) coated with cartilage, which you will learn matches the anterior surface of the tooth, which is also coated with cartilage.”