Physician, surgeon, and philosopher born in Pergamon, Galen combined animal dissection — Roman law forbade opening human cadavers —, clinical observation, and teleological philosophy from Plato and Aristotle. He identified seven pairs of cranial nerves, described heart valves and the structural differences between veins and arteries, and demonstrated via vivisection that arteries contain blood, not just pneuma as Erasistratus held. His extensive studies, from anatomy to pharmacology, dominated medical practice in Europe and the Islamic world for over a thousand years.