<P> The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis that supplies blood to the brain and surrounding structures . It is named after Thomas Willis (1621--1675), an English physician . </P> <P> The circle of Willis is a part of the cerebral circulation and is composed of the following arteries: </P> <Ul> <Li> Anterior cerebral artery (left and right) </Li> <Li> Anterior communicating artery </Li> <Li> Internal carotid artery (left and right) </Li> <Li> Posterior cerebral artery (left and right) </Li> <Li> Posterior communicating artery (left and right) </Li> </Ul> <Li> Anterior cerebral artery (left and right) </Li>

How many arteries make up the circle of willis
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