- Heinrich von Staden
Herophilus of *Chalcedon (c. 330–260 bce), Alexandrian physician, pupil of *Praxagoras of Cos. He and *Erasistratus were the only ancient scientists to perform systematic scientific dissections of human cadavers. If the controversial but unequivocal evidence of several ancient authors is to be trusted, Herophilus also performed systematic vivisectory experiments on convicted criminals—experiments made possible, according to A. *Cornelius Celsus, only by royal intervention (see vivisection). Herophilus' numerous anatomical achievements included the discovery of the nerves. He distinguished between sensory and ‘voluntary’ (motor) nerves, described the paths of at least seven pairs of cranial nerves, and recognized the unique characteristics of the optic nerve. The first to observe and name the calamus scriptorius (a cavity in the floor of the fourth cerebral ventricle), he called it κάλαμος (‘reed pen’) because it resembles the carved out groove of a writing pen. His dissection of the eye yielded the distinction between cornea, retina, iris, and chorioid coat.