Andreas Vesalius

Vesalius published De Humani Corporis Fabrica in 1543, based on his own dissections of human cadavers rather than the animal dissections and secondhand descriptions earlier anatomists such as Galen had relied on. The book corrected hundreds of errors in the Galenic anatomy that had gone unchallenged for over a thousand years, among them the number of bones in the human jaw and the pores Galen's model of the blood required in the wall between the heart's ventricles. Vesalius taught anatomy at Padua by performing dissections himself in front of students rather than reading from a text while an assistant cut, making direct observation the basis of the field.