Herophilus of Chalcedon, together with Erasistratus, founded in Alexandria the first documented tradition of systematic human dissection, made possible by the patronage of the early Ptolemies. He made the fundamental distinction between cerebrum and cerebellum, identified the brain as the seat of intelligence (against the Aristotelian tradition that placed it in the heart), described the cerebral ventricles, the calamus scriptorius, and the venous confluence that bears his name (torcular Herophili). He identified and named the duodenum (twelve finger-widths long), described the female ovaries as analogous to the male testes, distinguished motor from sensory nerves, and was the first to systematically measure the pulse with a water clock (clepsydra), establishing diagnostic correlations. His works were entirely lost; they are known only through citations by Galen, Celsus, Soranus, and Dioscorides. Later Galenic medicine eclipsed him and Erasistratus for more than a thousand years.