see more

Rene Descartes' diagram of the human brain and eye, 1692. From Opera Philosophica by Rene Descartes. (Frankfurt-am-Main, 1692). Originally published in his Tractatus de homine. (Paris, 1664). (Photo by Oxford Science Archive/Print Collector/Getty Images)

Rene Descartes' diagram of the human brain and eye, 1692. From Opera Philosophica by Rene Descartes. (Frankfurt-am-Main, 1692). Originally published in his Tractatus de homine. (Paris, 1664). (Photo by Oxford Science Archive/Print Collector/Getty Images)