(Chapter 4) Footnote 8:

Vesalius cites De partibus animalium 2.9 (“There is no such thing as a bone in isolation; every other bone is either actually part of the connected scheme, or else is attached to it and so is in contact with it” Loeb trans. by A.L. Peck) and Historia animalium 3.9. Vesalius’ point is that the basic interconnectedness of the bones is more important than the fact that the connection is not always direct. For the origin of bones from the spine, see Hist. an. 3.7.