Vertebral artery
The vertebral arteries are branches of the subclavian arteries. They arise, one on each side of the body, then enter deep to the transverse process of the level of the 6th cervical vertebrae (C6). It then proceeds superiorly, under the transverse process of each cervical vertebra until C1 where it enters the skull via the foramen magnum. Inside the skull, the two vertebral arteries join up to form the basilar artery at the base of the medulla oblongata. The basilar artery is the main blood supply to the brainstem and connects to the Circle of Willis to potentially supply the rest of the brain if there is compromise to one of the carotids.
At each cervical level, the vertebral artery sends branches to the surrounding musculature via anterior spinal arteries.