(Chapter 19) Footnote 44:

Vesalius cites book 8 of De anatomicis administrationibus and chapter 13 of De ossibus. See De anat. adm. 654: “in larger animals, [the ribs become] bony cartilage [towards the front] . . . [the false ribs] have a cartilaginous tendency, but at the ends are actual cartilages.” (Tr. Singer 1956, p. 202.) In De ossibus, he writes “As [the superior ribs] turn, they cease to be bone and become cartilage. The remaining five ribs, called “false,” . . . terminate in fine cartilage.” (2.765.7-10, tr. Singer 1952, p. 773).