Physician and scientist from Chalcedon, who was active in Alexandria in the 3rd century BC. He had studied medicine on the island of Hippocrates, Kos, and was to become the greatest physician in Alexandria.

By dissecting animals and human corpses, he learnt a lot about anatomy. He was especially fascinated with the human brain, and concluded that it was the centre for thinking and the nervous system, something Aristotle would have disagreed on.

Herophilos also found a difference between the veins and the arteries, and said that the pulse is the result of the contractions and expansions of the arteries. He did not, however, see the connection with the heart.

In order to measure the pulse he invented a clepsydra: a portable water clock. He also named the cornea, retina and the duodenum.