circle of Willis
A circle of arteries that supply blood to the brain. The Circle of Willis comprises the following arteries: Anterior cerebral artery (left and right); Anterior communicating artery; Internal carotid artery (left and right); Posterior cerebral artery (left and right); Posterior communicating artery (left and right).The basilar artery and middle cerebral arteries, supplying the brain, are also considered part of the circle.