Herophilus, a pupil of Praxagoras of Cos, was one of the founders of the Alexandrian medical school set up at the end of the 4th century bc under the patronage of Ptolemy I Soter. Although none of his works have survived, Galen lists some eight titles of which the Anatomica (Anatomy) was probably the most significant.

Herophilus is widely, even notoriously, remembered as the result of a passage in Celsus reporting that, with Erasistratus, he practiced vivisection on criminals. The passage has been regarded as suspect by many scholars on the grounds that no such reference occurs in any extant, earlier Greek text. It is however certain that from the results attributed to him he must have undertaken both human and animal dissection. For example, he described a passage from the stomach to the intestines as being ‘12 finger widths’ (dodekadaktylon) or in its Latin form, the duodenum; he also named the retina and the prostate and did much work on the brain.

It has been claimed that Herophilus was the first to distinguish between sensory and motor nerves. Nerves, or neura, for Herophilus were simply channels that carried the pneuma or vital air to different parts of the body. Thus while he probably identified sensory nerves it is unlikely that he was able to distinguish between motor nerves and tendons.

Herophilus was reported to have advanced Praxagoras's work on the pulse by counting its frequency against a water clock. Also, according to Galen, he made the important observation that the arteries carried blood as well as pneuma.