(Chapter 29) Footnote 2:

Because Vesalius follows Greek tradition in regarding the acetabulum or hip joint as a whole as part of the ischium (rather than the place where the three pelvic bones fuse), he regularly uses coxendix or os coxendicis, “hipbone,” in referring to the ischium alone. See n. 3 below. This translation preserves Vesalius’ use of “hipbone,” which should not be confused with the modern use of the word to refer to the os coxae or innominate bone, a fused combination of three pelvic bones.