Book excerpt: Galen of Pergamon, was a prominent Roman physician, surgeon and philosopher. The most accomplished of all medical researchers of antiquity, Galen contributed greatly to the understanding of numerous scientific disciplines, including anatomy, physiology, pathology, pharmacology, and neurology, as well as philosophy and logic. Galen's understanding of anatomy and medicine was principally influenced by the then current theory of humorism, as advanced by many ancient Greek physicians such as Hippocrates. His theories dominated and influenced Western medical science for more than 1,300 years. Medical students continued to study Galen's writings until well into the 19th century. Galen conducted many nerve ligation experiments that supported the theory, which is still accepted today that the brain controls all the motions of the muscles by means of the cranial and peripheral nervous systems.