Circle of Willis
The circle of Willis is the anatomical name given to the formation of arteries at the base of the brain that contribute the overwhelming majority of blood supply to the brain.
The circle of Willis is formed by the connections between the predominantly horizontal branches that derive from the middle cerebral arteries anteriorly and from the basilar artery posteriorly. The right and left middle cerebral arteries each give off an anterior cerebral artery (forming the anterolateral borders of the circle of Willis), which goes forward to supply blood to the frontal lobe. These anterior cerebral arteries are connected to each other by the anterior communicating artery, which forms the front of the circle. Posteriorly, the basilar artery bifurcates into the right and left posterior cerebral arteries, which supply the occipital and posterior temporal lobes and the cerebellum, forming the posterior border of the circle. Each posterior cerebral artery is connected to...