Internal carotid artery is known as the carotid sinus or the carotid bulb. The ascending portion of the cervical segment occurs distal to the bulb, when the vessel walls are again parallel. The internal carotid runs vertically upward in the carotid sheath and enters the skull through the carotid canal. During this part of its course, it lies in front of the transverse processes of the upper three cervical vertebrae. It is relatively superficial at its start, where it is contained in the carotid triangle of the neck, and lies behind and medial to the external carotid, overlapped by the sternocleidomastoid muscle, and
Common carotid artery are separated from each other by a very narrow interval which contains the trachea; but at the upper part, the thyroid gland, the larynx and pharynx separate the two arteries. The common carotid artery is contained in a sheath known as the carotid sheath, which is derived from the deep cervical fascia and encloses also the internal jugular vein and vagus nerve, the vein lying lateral to the artery, and the nerve between the artery and vein, on a plane posterior to both. On opening the sheath, each of these three structures is seen to have a separate fibrous cover.