(Chapter 17) Footnote 14:

Vesalius’ marginal note cites book 13 of De usu partium and chapter 10 of De ossibus. In book 12 of De usu partium 4.66.18 Galen had said that the lumbar vertebra has nine processes as opposed to seven thoracic processes (May 1968, p. 582). In book 13 he adds “the large ones [viz. the lumbar vertebrae] have two additional outgrowths [the accessory processes] slanting downward. For since the articulations of the vertebrae are made by the outgrowths that slant downward and rest upon those that slant upward, Nature for the sake of safety has placed under the whole articulation a second outgrowth slanting downward ... But if to the three outgrowths I have mentioned (the largest of all [the spinous process], which forms the acantha, and the two transverse) you add the two slanting upward and the four slanting downward, it is evident there are nine in all. ... there are indeed precisely this number of outgrowths of just these kinds that do belong to the lumbar vertebrae.” (4.74.15-75.12, tr. May 1968 p. 586). In Chapter 10 of De ossibus Galen mentions in the lumbar vertebrae “a large downward-tending apophysis where the nerves emerge.” (§761, tr. Singer 1952 p. 772).