Doctor to Roman gladiators and emperors, Galen was a Greek physician in the 2nd century CE whose authority on medicine was virtually undisputed until the 16th century. Credited with some 500 treatises, Galen added greatly to the knowledge of anatomy and physiology. Based on animal experiments, he described cranial nerves and heart valves and showed that arteries carry blood, not air. However, in extending his findings to human anatomy, he was often in error. What misconceptions did he have? Discuss