The two common carotid arteries arise from the innominate artery in the manner already described. Each passes craniad along the side of the trachea. In the thorax (Fig. 118, _f_) the common carotid lies mediad of the subclavian artery (Fig. 118, _c_) and dorsad of the superior vena cava (Fig. 118, _q_). In the neck (Fig. 119) the artery lies, accompanied by the vagus and sympathetic nerves and the internal jugular vein (_b_), in the space between the longus capitis muscle (7) and the trachea (14); it is covered ventrally by the sternomastoid and sternothyroid (2) muscles, lying close to the lateral border of the latter. Near its origin the common carotid may give rise to the small =inferior thyroid= artery. It then passes to about the level of the larynx without giving off branches; here it gives off the =superior thyroid= (_c_) on the ventral side and one or more muscular branches (_e_) on the dorsal side. One or two centimeters further craniad it gives off on the dorsal side the =internal carotid= (_g_) and the occipital artery (_f_). The main artery now takes the name =external carotid= (_m_). [Illustration: FIG. 119.--COMMON CAROTID ARTERY AND INTERNAL JUGULAR VEIN. _a_, common carotid artery; _b_, internal jugular vein; _c_, superior thyroid artery; _d_, cervicalis ascendens artery; _e_, large muscular branches; _f_, occipital artery; _g_, internal carotid; _h_, branch to larynx; _i_, lingual artery; _j_, external maxillary; _k_, superior labial; _l_, inferior labial; _m_, external carotid; _n_, internal maxillary; _o_, posterior auricular; _p_, superficial temporal. 1, M. sternohyoideus; 2, M. sternothyreoideus; 3, M. geniohyoideus; 4. M genioglossus; 5, M. constrictor pharyngis medius; 6, M. constrictor pharyngis inferior; 7, M. longus capitis; 8, M. digastricus; 9, M. masseter; 10, M. scalenus; 11, M. levator scapulæ (cut); 12, M. levator scapulæ ventralis (cut); 13, M. splenius; 14, trachea.] Branches of the common carotid: 1. =A. thyreoidea ima.=--The inferior thyroid is a small artery which arises either from the common carotid near its origin, or from the innominate before the origin of the carotid. It passes craniad on the trachea as far as the thyroid gland, giving branches to the trachea and œsophagus. 2. =A. thyreoidea superior= (_c_).--The superior thyroid leaves the carotid opposite the thyroid cartilage and passes mediad and caudad, sending branches to the thyroid gland, and the sternothyroid (2) and sternohyoid (1) muscles. A small branch, the =superior laryngeal=, passes to the larynx, and supplies those muscles of the larynx which are not enclosed by the cartilages. 3. =Rami musculares= (_e_).--One or two branches, usually of considerable size, leave the common carotid at about the same level as the superior thyroid and pass to the muscles on the dorsal side of the neck, the main trunk of the artery passing between the longus capitis (7) and scalenus muscles (10).