either in a humane body, or in an apes ; ‘tis best in both ; and then to go to the anatomy of the muscles.”" (edward tyson, orang-outang..., 1699, p. 59.) up until that point, galen and his teachings had been the authority on human anatomy. the irony is that galen himself had emphasized the fact that one should make one's own observations instead of using those of another, but this advice was lost during the numerous translations of his work. as vesalius began to uncover these mistakes, other physicians of the time began to trust their own observations more than those of galen. an interesting observation made by some of these physicians was the presence of homologous structures in a wide variety of animals which included humans. these observations were later used by darwin as he formed his theory of natural selection.