Today, René Descartes (1596–1650) is mainly known because of his contributions to mathematics and philosophy. But he was highly interested in anatomy and physiology as well. He paid so much attention to these subjects that it has been suggested that “if Descartes were alive today, he would be in charge of the CAT and PET scan machines in a major research hospital” (Watson 2002, p. 15). Descartes discussed the pineal gland both in his first book, the Treatise of man (written before 1637, but only published posthumously, first in an imperfect Latin translation in 1662, and then in the original French in 1664), in a number of letters written in 1640–41, and in his last book, The passions of the soul (1649).