Illustration from a book by Rene Descartes De Homine, published after his death in 1662. It is regarded as the first textbook of physiology. The picture shows the supposed relationship between the sensory perception of an image & muscular action. The image is relayed from the eyes to the pineal gland (H). The reaction between the image & the pineal gland determines the motor action, driven from c. Descartes concludes that the relationship between b (reception of the signal) & c (action) is an insoluable mystery, wrapped up in the very nature of the soul". Descartes, a French philospher & mathematician, lived from 1596-1650"