 Alcmaeon’s empiricism has sometimes been thought to have arisen from his experience as a practicing physician (Guthrie 1962). He has also been hailed as the first to use dissection, but this is based on a hasty reading of the evidence. Calcidius, in his Latin commentary on Plato’s Timaeus, praises Alcmaeon, along with Callisthenes and Herophilus, for having brought many things to light about the nature of the eye (DK, A10). Most of what Calcidius goes on to describe, however, are the discoveries of Herophilus some two centuries after Alcmaeon (Lloyd 1975, Mansfeld 1975, Solmsen 1961). The only conclusions we can reasonably draw about Alcmaeon from the passage are that he excised the eyeball of an animal and observed poroi (channels, i.e. the optic nerve) leading from the eye in the direction of the brain (Lloyd 1975). Theophrastus’ account of Alcmaeon’s theory of sensation implies that he thought that there were such channels leading from each of the senses to the brain: