Footnote 22:

The 1555 edition adds “who were certainly no obscure physicians.” In Vesalius’ Letter on the China Root (1546) and in the charter creating him a count Palatine in 1556, we learn that his great-great-grandfather Peter Witing had written a treatise on the fourth Fen of Avicenna and attended on the emperor Frederick III. Though none of this has been verified and Peter remains a shadowy, perhaps mythical figure, Vesalius’ great-grandfather John was a professor of medicine at Louvain and city physician for Brussels; his grandfather Everard was physician to the Archduke Maximilian and wrote learned commentaries on Rhazes and Hippocrates. See O’Malley AVB pp. 21-27.