The OED for a start....
Its safe to say that at the time the book was written, and the edition you are using, ancle was an accepted spelling of ankle.
Unfortunately I'm currently unable to access my library's web site, so can't get back to the OED. Hopefully I'll be able to in the morning,
This link should work for the next 3 days.
http://www.oed.com/view/Entry/7823?p...N1z5ijg&d=7823