By careful and painstaking dissections of cadavers, he learned a great deal about the structure of the human body and laid the foundation for modern physiology.
In 1543, he published a remarkable book 'De humani corporis fabrica'. It was a fully illustrated anatomy of the human body, based on the observations Vesalius had made during his dissections. The book destroyed the misconceptions in anatomy that had persisted for over a thousand years.
Vesalius' anatomical studies corrected many religious beliefs and the finding of a previous physician Galen, who had dissected apes because religion forbade him to dissect real human cadavers.
Vesalius was the first surgeon to actually cut open a cadaver or dead body of a human being, and his exceptionally detailed muscle drawings changed medical history for all time.