around the same time, andreas vesalius was also making some strides of his own. a young anatomist of flemish descent made famous by a penchant for amazing charts, he was systematically investigating and correcting the anatomical knowledge of the greek physician galen. he noticed that many of galen's observations were not even based on actual humans. instead, they were based on animals such as apes, monkeys, and oxen. in fact, he entreated his students to do the following, in substitution for human skeletons, as cited by edward tyson : "“if you cant happen to see any of these, dissect an ape, carefully view each bone, &c. …” then he advises what sort of apes to make choice of, as most resembling a man : and conclude “one ought to know the structure of all the bones