The common carotid arteries are present on the left and right sides of the body. These arteries originate from different arteries but follow symmetrical courses. The right common carotid originates in the neck from the brachiocephalic trunk; the left from the aortic arch in the thorax. Each of the two arteries pass up the side of the neck and divide opposite the upper border of the thyroid cartilage into an external branch supplying the face, tongue, and external parts of the head and an internal branch supplying the brain, eye, and other internal parts of the head. If these arteries were blocked for any reason, it would prevent blood getting to the brain leading to syncope (passing out or "deep sleep") or, if blocked long enough, death.