Andreas Vesalius wrote De Humani Corporis Fabrica Libri Septum, which revolutionized medicine. The seven volume work was the most detailed text on human anatomy. Vesalius was able to get bodies for dissection and this enabled him to give descriptions of the human body. Many of his discoveries disproved Claudius Galen's medical assertions. Galen's concepts had been dominant since the Roman Empire. Galen did not have the advantage of cadavers for dissection. The impressive element of Vesalius' work is the detailed illustrations of organs and their systems. The image of the human brain is the most incredible. The illustration shows the base of the brain. What can be seen are the cerebellum, olfactory bulbs, and optic nerves. The left and right hemispheres show both fissures and convolutions. The drawing is precise to a contemporary medical text. What was missing from Humani Corpis Fabrica was the depiction of neurons. The reason was a limitation of technology. Andreas Vesalius did not have access to a microscope. Without such tools certain parts of the human body could not be detected. Vesalius did not fully comprehend the brain's physiology. The understanding of neurotransmitters and electrical impulses through the brain cells would come centuries later. Surgeons and doctors probably had a suspicion that the brain was responsible for the senses. The challenge was proving transduction to be true. The human brain is the most complex organ of the body. It controls movement, consciousness, thought, and involuntary biological function. There is more to uncover about this intricate organ. Vesalius put emphasis on an observational methods. The teaching of medicine and surgery changed to a more empirical approach.