Borelli, student of Galileo and teacher of Malpighi, applied his knowledge of mathematics, chemistry, and physics to the explanation of physiological phenomena, such as respiration, digestion, and the secretion of urine, but especially, as described in De motu animalium, to the motion of animals and the coordinated action of flexor and extensor muscle groups.1 A Neapolitan by birth, he studied mathematics at Rome under Castello. In his early 30's he was called to the University of Messina as professor of mathematics, where he prepared an account of the plague in Sicily. Later he filled a similar post at the University of Pisa at the prime period of the Medicis' promotions of the sciences and the arts. Although Borelli probably gave some attention to medical practice in each community, there is no record of apprenticeship and he devoted most of his talents to teaching mathematics and medical science. On the