 Vesalius' most famous work, "De humani corporis fabrica", was greatly influenced by Galenic writing and form.Seeking to examine critically Galen's methods and outlook, Vesalius turned to human cadaver dissection as a means of verification.Galen's writings were shown by Vesalius to describe details present in monkeys but not in humans, and he demonstrated Galen's limitations through books and hands-on demonstrations despite fierce opposition from orthodox pro-Galenists such as Jacobus Sylvius.