Here is a diagram of vascular anatomy.
The main branches of the internal carotids are the middle and anterior cerebral arteries (anterior circulation).
The internal carotids supply blood to the anterior three-fifths of the cerebrum:
The vertebrobasilar arteries supply the posterior two-fifths of the cerebrum:
They also supply part of the cerebellum and the brain stem (posterior circulation).
The basilar artery formed by the union of the two vertebral arteries gives off the posterior cerebral arteries.
The common carotids each divide into two branches:
The arch of the aorta is the portion between the ascending and descending aorta. The left common carotid originates directly off the highest part of the arch.