(Chapter 15) Footnote 51:

See chapter 8, §462: “Lateral bends of the head are made by 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.” (tr. Singer 1956, p. 113).