Thomas Willis and circle of arteries

In 1664 the British scientist Thomas Willis (1621-1675) described in his treatise about a circle of arteries at the base of the brain that act as a traffic for the blood flowing to the head. Willis landmark text, Cerebri Anatome , 1664, was reproduced many times and developed into a pocket-sized standard textbook for medical students. The circle of Willis provides a potential diversion for collateral blood supply following the occlusion of one major cranial arteries feeding, into it. Because of