(Chapter 17) Footnote 22:

Vesalius cites Book 13 of De usu partium and Book 5 of De anat. adm. in his margin. For the passage in De usu partium where Galen describes the accessory processes, see note 14 above. The passage in De anat. admin. which Vesalius seems to have in mind describes the lumbar iliocostal muscles. See the end of Book 5 (2.530.19ff.): “These muscles draw down the last ribs. In other animals they extend as far as the third and fourth ribs, counting the ribs from below; but in apes they reach [only to] the second and third of the so-called false ribs, sometimes only the latter. Anatomists have overlooked them too [as well as the spinal muscles starting from 2C], cutting away part of them, I think, with the eight abdominal muscles, and leaving the other part adhering to the spinal muscles.” (tr. Singer 1956, p. 146).