(Chapter 16) Footnote 39:

Vesalius cites De ossibus and book 13 of De usu partium: “their spines, as far as the tenth vertebra, are much like those of the cervical, sloping downward but from the tenth they begin to slope the other way, in the tenth indistinctly, but more plainly in the others.” (De ossibus 759-760, tr. Singer 1952 p. 772); in De usu partium Bk. 13, Galen says “the middle vertebra [the tenth thoracic] is the only one properly to have its posterior outgrowth straight and not inclined.” (4.78.9-11, tr. May 1968, p. 588). Cf. 4.63.14 (tr. May 1968 p. 580), which May notes is “proof positive that Galen is describing the simian spine, in which the spinous process of the tenth thoracic vertebra is indeed horizontal, whereas all above it are directed obliquely downward and those below, upward.” (n. 59).