Illustration of the pineal gland from a book by Rene Descartes entitled De Homine, published after his death in 1662. The book is regarded as the first textbook of physiology. Descartes believed that the pineal gland, marked H in this picture, was the seat of the soul. A French philosopher and mathematician, Descartes was born in 1596 and died, in Sweden in 1650.