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Definition of Willis, circle of
Medically reviewed by Min Clinic Staff | Updated: January 2026
Willis, circle of: A critical arterial circle at the base of the brain. The circle of Willis receives all the blood that is pumped up the two internal carotid arteries that come up the front of the neck. All the principal arteries that supply the two halves of the brain (hemispheres) branch off from the circle of Willis.