(Chapter 30) Footnote 18:

“not far from the origin of whose head is attached the sesamoid ossicle whose smooth and slippery surface, rising above the substance of the muscle, faces toward the smooth region of the inner head of the femur and receives its hard contact and in the common way of sesamoid bones distributes its impact.” (1555). Vesalius may have written “inner head” when he meant “outer” ; an articular sesamoid or fabella may occur in the m. gastrocnemius, caput laterale, found behind the lateral femoral condyle ( Gray 1995, p. 736).