 One of the best known examples of Vesalius' overturning of Galenism was his demonstration that the interventricular septum of the heart was not permeable, as Galen had taught ("Nat Fac III xv").However, this had been revealed two years before by Michael Servetus in his fateful ""Christianismi restitutio"" (1553) with only three copies of the book surviving, but these remaining hidden for decades; the rest were burned shortly after its publication because of persecution of Servetus by religious authorities.Michael Servetus, using the name "Michel de Villeneuve" during his stay in France, was Vesalius' fellow student and the best Galenist at the University of Paris, according to Johann Winter von Andernach, who taught both.