The basilar artery is formed by the fusion of which arteries?

• A. Internal carotid arteries
• B. External carotid arteries
• C. Subclavian arteries
• D. Vertebral arteries

Answer: (D)

The basilar artery is formed by the fusion of the two vertebral arteries. Each vertebral artery branches off the subclavian artery, ascends through the cervical spine, enters the skull, and then they join at the lower part of the brainstem (the pons) to create the basilar artery. This artery then runs along the ventral surface of the pons and supplies parts of the brainstem, cerebellum, and posterior cerebral circulation.

The other vessels don’t form the basilar artery: the internal carotid arteries contribute to the anterior circulation via the circle of Willis, the external carotid arteries supply the face and neck, and the basilar artery itself is specifically the fusion product of the vertebral arteries rather than a direct fusion of the subclavian or carotid systems.