Illustration of Galen (130-200 AD), Ancient Greek physician. After Galen's death, his body of work became a medical authority among Europeans until his views on anatomy were overthrown in the 16th century by Vesalius, and those on physiology in the 17th century by Harvey. In Galen's time, human dissection was taboo, and Galen's anatomical assumptions, which were based on animals, were not, as it was later seen, always applicable to humans. He was the first to use the pulse as a diagnostic aid and the first to describe the flow of urine through the ureters to the bladder. Illustration from 1866.