People have probably known the basic features of the human and animal body since prehistoric times. Many physicians of ancient Greece and Rome were aware that knowledge of human anatomy might be crucial to effective treatment. However, it was not until the 16th century that it became clear that the only way to understand human anatomy in detail was by studying the human body itself.
This seems obvious now, but when the Flemish physician Andreas Vesalius pioneered this approach in the 16th century by dissecting human corpses, it was revolutionary. Physicians at the time did not believe in dissecting bodies, thinking they could obtain most of what they needed to know from the works of the ancient Roman physician Galen. But Vesalius, through his insistence on trusting only solid observations of the real thing, completely changed our knowledge of the human body.
Vesalius’s detailed work also began to pin down how human anatomy differed from that of animals—and what they had in common. This focus on the details of variations in anatomy between species led to the development of the science of comparative anatomy, enabling the classification of animals into groups of related species. It eventually provided the basis for British naturalist Charles Darwin’s theory of evolution.
The Dissection Taboo
One of the problems for early human anatomists was the taboo on the dissection of corpses. The 5th-century BCE Greek anatomist Alcmaeon tried to get around this by dissecting animals. In the following century, the city of Alexandria was an exception; anatomists there were allowed to dissect human cadavers. Herophilus, one such anatomist, made many key observations this way. He correctly asserted that the brain, rather than the heart, is the seat of human intelligence, and he identified the role of nerves. Herophilus went too far even for Alexandrians, however, when he conducted dissections on living criminals.
Received Wisdom
Galen drew heavily on the work of Herophilus for his highly influential treatises "On Anatomical Procedure" and "On the Uses of the Parts of the Human Body," which he compiled using the results of his own dissections and vivisections of animals. One of his most important discoveries was that arteries are filled with flowing blood, not air, as had previously been thought. He also learned much in his role as chief physician to the gladiators, which gave him a close-up view of some terrible combat wounds. His work was so detailed and comprehensive that Galen’s reputation was unassailable for the next 1,400 years.
Even in Vesalius’s time, lecturers would read from Galen’s texts to instruct students while, in the background, barber surgeons dissected the bodies of executed criminals as instructed, and assistants pointed out the features that the lecturer was describing. It was always assumed that Galen was correct, even if the text did not appear to match what the students saw in the cadaver. Vesalius questioned Galen from the start of his career. He began his medical education in Paris under anatomists with full faith in Galen, and the lack of practical anatomy classes frustrated Vesalius. He completed his degree in Padua, where he began to dissect human corpses so he could learn anatomy firsthand, rather than relying on Galen’s texts. He had a sharp eye for detail and produced highly accurate anatomical drawings of the blood and nervous systems.
His 1539 pamphlet showing the blood system in detail had instant practical benefits for physicians who needed to know where to take blood from—at the time, bloodletting was at the heart of medical practice. Vesalius’s reputation soared, and he was made a professor of surgery and anatomy when he graduated. A Paduan judge guaranteed him a supply of cadavers—the bodies of hanged criminals. With these at his disposal, he was able to make repeated dissections for research and for student demonstrations.
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