Final answer:
The arterial vasa corona above C3 is formed at the base of the brain by the circle of Willis, a network of arteries that is fed by the vertebral and internal carotid arteries, and includes the anterior and posterior cerebral and communicating arteries.
Step-by-step explanation:
The arterial vasa corona above C3 is formed by the anastomosis of vessels at the base of the brain, known as the circle of Willis or arterial circle. The circle of Willis is composed of internal carotid and vertebral artery branches. Specifically, above the level of C3, the vertebral arteries, which arise from the subclavian arteries and pass through the vertebral foramen, ascend through the foramen magnum to the brain. These arteries join with the internal carotid arteries to form the arterial circle, thereby providing a continual blood supply to the brain.
The circle of Willis is further detailed by its anterior and posterior portions. The anterior part comprises of the anterior cerebral arteries joined together by the anterior communicating artery. The posterior portion is made up of the posterior communicating arteries branching from the posterior cerebral arteries, which themselves arise from the basilar artery that begins at the junction of the two vertebral arteries.