Galen’s emphasis on the practice of dissection and vivisection led him to write both short introductions to anatomy and a long procedural guide that includes detailed directions on how to anatomize animals, both living and dead. His assumption was that his readers would have an actual animal’s body at the ready, and thus none of his books included illustrations. As Galen’s writings were passed down through time—translated, consolidated, abridged, and elaborated—later thinkers began to add anatomical illustrations. Among the earliest surviving examples is a series of five squatting figures, each representing different human bodily systems: veins, arteries, bones, nerves, and muscles. Also drawn on each figure are the specific organs Galen associated with that system. The origins of these figures are obscure, but they spread across the medieval world, with examples surviving from England to Iran and attached to texts in Latin, Provençal, Persian, and Arabic, the dominant language of medical discourse in the early medieval period.
Galen’s influence in the medieval Islamic world is pronounced. His anatomical and physiological writings were translated into Arabic in the ninth and tenth centuries and had a profound and pervasive impact on subsequent conceptions of the body. They were also modified and revised: Ibn al-Nafis al-Qurashi, for example, questioned aspects of Galen’s description of pulmonary circulation, arriving at a theory more similar to our modern understanding. Perhaps one of the most important books that systematized, modified, and developed Galenic medical theory is The Canon of Medicine by Ibn Sina (Avicenna). Widely read among physicians in the Islamic world, it was commonly used in its Latin editions as a textbook for medical training in European universities and inspired a new medical literature of abridgments, epitomes, and commentaries.
While many of these thinkers refined or critiqued Galen’s works, his anatomy remained authoritative and went largely unchallenged until the appearance in 1543 of On the Fabric of the Human Body in Seven Books by the Flemish-born anatomist Vesalius. Although his findings overturned many of Galen’s theories and he is credited as establishing modern anatomy, Vesalius was in fact following Galen’s order to perform dissections personally, and his commitment to direct observation in pursuit of proof was unquestionably Galenic. Vesalius realized that some of Galen’s errors resulted from his need to rely on animals rather than cadavers. Working in the Renaissance, when the prohibition against human dissection was losing some of its edge, he was able to dissect human bodies, although reactions at the time were mixed. Some readers immediately recognized Vesalius’s work as corrective and declared his anatomy a masterpiece, while Galen loyalists were scandalized by what they perceived as disrespect for the ancient master. Over time, Vesalius’s anatomy came to replace Galen’s in its influence, and the woodcuts from On the Fabric of the Human Body (likely by the artist Jan van Calcar, a student of Titian) have also inspired generations of medical illustrators.