Blood supply to the head and neck is provided by the common carotid arteries and branches of the subclavian artery. The common carotid arteries, which have the broadest distribution, divide into the external and internal carotid arteries. The external carotid arteries reach most tissues of the head, except for the brain and orbits. They branch into various smaller arteries supplying the thyroid gland, larynx, tongue, anterior face, posterior scalp, and jaws. The internal carotid arteries supply over 80% of the cerebrum and the orbits. They enter the cranium and branch into the ophthalmic artery, which further divides into the anterior and middle cerebral arteries. From the subclavian arteries, the vertebral arteries rise in the neck, and their branches reach the vertebrae, spinal cord, and several deeper neck structures. Inside the cranium, the right and left vertebral arteries merge, forming the basilar artery, which supplies blood to the cerebellum, pons, and inner ear. The thyrocervical and costocervical trunks from the subclavian artery supply the thyroid gland, cervical vertebrae, spinal cord, scapular muscles, neck, and superior intercostal muscles.