The carotid artery carries blood to the head and brain. The pulsation of the common carotid artery can be felt on the surface of the neck, medial to the sternocleidomastoid muscle. The carotid artery can be divided into two segments from thick to thin. The first segment is called the common carotid artery, and the second segment is divided into the internal and external carotid arteries by the common carotid artery. The common carotid artery is the arterial trunk of the head and neck, and there is one common carotid artery on the left and right side of the neck, called the left and right common carotid artery, respectively. Most of the left common carotid artery originates from the aortic arch, and most of the right common carotid artery originates from the cephalic trunk. The cephalothoracic trunk originates from the ascending aortic arch, which in turn gives rise to the right common carotid artery and the right subclavian artery. In a few individuals, there is anatomic variation in the cephalic trunk and common carotid artery. Both common carotid arteries run posteriorly along the sternoclavicular joint, lateral to the esophagus, trachea, and larynx, and upward to the superior border of the thyroid cartilage where they divide into the internal and external carotid arteries. The external carotid artery first resides on the anteromedial side of the internal carotid artery, and the internal carotid artery resides on the posterior lateral side. When the neck is turned, a very obvious muscle can be found from the ear to the upper edge of the sternum, which is the sternocleidomastoid muscle. On the medial side of the sternocleidomastoid muscle, the pulsation of the carotid artery can be felt. When the patient faints, if the carotid artery is not touched, it means that the heart stops and emergency cardiopulmonary resuscitation is needed.