The circle before willis: a historical account of the intracranial anastomosis.

The circle of Willis is one of the most famous eponymous structures in human anatomy. There is no doubt Thomas Willis at Oxford accurately demonstrated the anastomotic arterial supply at the base of the brain. However, this eponymous name does not reveal the history of the discovery of the ramification, nor does it give credit to the anatomists and artists who have contributed to the understanding of this clinically important structure. This article first traces the story of the discovery of the circle of Willis. Willis' contribution and innovative approaches are then discussed. Finally, despite Willis' not being the first to describe the circle, we explain why he still deserves to retain the eponymous title. The earlier description of the vasculature at the base of the brain was fixated on a nonexistent structure, at least not in humans, named the rete mirabile. The more scientific study of the blood supply to the brain took place during the Renaissance period, which culminated in the work of Thomas Willis in the 17th century.