(Chapter 15) Footnote 92:

Vesalius cites book 4 of De anatomicis administrationibus, where in chapter 8 Galen discusses the movements of the first and second vertebrae: “Lateral bends of the head are made by the oblique muscles. They incline it to one side or the other of the condyles, to whichever the muscle stretching it leads. There the head is firmly fixed in the facet [of the atlas], pressing the condyle into it, and floats on the other and higher condyle mounted in the opposite facet.” (4.8.462-463, translated by Singer 1956, p. 113)