Circle of Willis
Figure 15. Circle of Willis. The blood supply to the brain enters through the internal carotid arteries and the vertebral arteries, up through the basilar artery, eventually giving rise to the circle of Willis. This arterial blood supply to the brain includes the following arteries seen in the figure: posterior cerebral artery, posterior communicating artery, middle cerebral artery (not part of actual Circle, though), anterior communicating artery and the anterior cerebral artery.
