The carotid artery is divided into the common carotid artery, the internal carotid artery and the external carotid artery. The right common carotid artery originates from the innominate artery and the left artery from the aortic arch. The internal diameter of the common carotid artery is about 6.2-7.2 mm, the internal diameter of the internal carotid artery is about 5.1-6.1 mm, and the internal diameter of the external carotid artery is about 4.1-5.1 mm. The internal carotid artery is mainly responsible for the blood supply to the anterior two-thirds of the brain, while the external carotid artery mainly supplies blood to various tissues and organs outside the skull. Even if the external carotid artery is narrowed, it will not show obvious clinical symptoms because there are more traffic branches on the contralateral and local sides and the compensation is obvious.