Illustration of cerebral vascularisation highlighting the circle of Willis. the arterial circle which irrigates the brain. This arterial vascularisation is made up of internal carotid arteries and the basilar artery. The internal carotid arteries lead to two cerebral arteries and the communicating artery. The basilar artery comes from the two vertebral arteries. Two cerebral arteries and two communicating arteries spring from here. The circle ensures the provision of nutriments and oxygen to the brain.