The two vertebral arteries and the basilar artery are known as the vertebral basilar system, which supplies blood to the posterior part of the circle of Willis and joins with blood supplied to the anterior part of the circle of Willis from the internal carotid arteries.

[4][5][6] The diameter of the basilar artery range from 1.5 to 6.6 mm.

[7] The basilar artery arises from the union of the two vertebral arteries at the junction between the medulla oblongata and the pons between the abducens nerves (CN VI).

It divides at the junction of the midbrain and pons into the posterior cerebral arteries.

[citation needed] Its branches from caudal to rostral include:[citation needed] A basilar artery stroke classically leads to locked-in syndrome.