Andreas Vesalius was first to revolutionize the Galenic system of human physiology. Appointed to teach human anatomy at the University of Padua in 1537, Vesalius taught anatomy while performing his own dissections. On the basis of these investigations, Vesalius enumerated over 200 errors in Galen's anatomical writings. His De humani corporis fabrica appeared in the same year as Copernicus' heliocentric cosmography; its voluminous descriptions and some 250 anatomical drawings amounted to an atlas to the inner world of the human body. His descriptions of the venous system (pictured here) contributed to the formation of a theory of pulmonary circulation. Image right: the venous system of the human body, as depicted in Andreas Vesalius' De humani corporis fabrica (1543). Image left: portrait of Andreas Vesalius, from his De humani corporis fabrica; Image source: Wikipedia Commons.