Medicine, which was dominated by the Hippocratic tradition, saw new advances under Praxagoras of Kos, who theorized that blood traveled through the veins. Herophilos (335–280 BC) was the first to base his conclusions on dissection of the human body, animal vivisection and to provide accurate descriptions of the nervous system, liver and other key organs. Inﬂuenced by Philinus of Cos (ﬂ. 250), a student of Herophilos, a new medical sect emerged, the Empiric school, which was based on strict observation and rejected unseen causes of the Dogmatic school.