The cervical portions of the common carotids resemble each other so closely that one description will apply to both. each vessel passes obliquely upward, from behind the sterna clavicle articulation, to the level of the upper border of the thyroid cartilage, where it divides into the external and internal carotid arteries. At the lower part of the neck the two common carotid arteries 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 project forward between the two vessels. The common carotid artery is contained in a 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 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 investment.