Diagram of the ventricles of the brain and pineal gland, L'Homme de René Descartes

Following Galen, the Greco-Roman surgeon and philosopher (129–199/217 CE), 17th-century attention concentrated on the ventricular system of the brain. The theorist René Descartes (1596–1650) maintained that the pineal gland was the seat of the soul and the governing centre of the human body, regulating the ‘spirits’ that connected via the ventricles to the muscles of the body. In this diagram of a transverse section of the brain, the pineal gland is indicated by the letter H and the areas I and B show the nerves running towards the ventricles (A).