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).
4. A. occipitalis (f).—The occipital artery arises from the common carotid at about the same point as the internal carotid. It immediately sends a large branch dorsad, passing between M. longus capitis (7) and the vertebral column, to the deep muscles of the neck. The occipital then crosses the outer surface of the digastric muscle (8) to the back of the skull, and runs along the lambdoidal crest just beneath the splenius muscle. It sends a number of branches to the muscles of the back of the neck; and one of its branches may unite with the vertebral artery as it lies in the groove on the atlas, or with a branch of the vertebral.
5. A. carotis interna (g).—The internal carotid artery is one of the terminal branches of the common carotid. It is very small. It is given off near or in common with the occipital artery, passes toward the cranial end of the tympanic bulla, enters the bulla with the Eustachian tube, and passes into the skull at the foramen lacerum. Its course is much convoluted before entering the foramen. Within the skull ([Fig. 121], g) it joins the posterior cerebral artery ([Fig. 121], f) at the side of the hypophysis.
6. A. carotis externa ([Fig. 119], m).—After giving off the internal carotid the continuation of the common carotid artery receives the name external carotid (m). It passes craniad and laterad between the digastric (8) and styloglossus muscles, where it gives off cranioventrad the lingual artery (i) and a number of small muscular branches; also sometimes the small laryngeal artery. At the dorsolateral border of the digastric (8) it gives off the external maxillary artery (j), and about one centimeter farther craniad the posterior auricular (o). It now turns mediad, lying against the cartilaginous auditory meatus, on its cranial side, and gives off the superficial temporal (p). The artery then continues mediad, taking the name internal maxillary (n)—so that the internal maxillary artery is to be considered the terminal branch of the external carotid.
Branches of the external carotid artery ([Fig. 119]):
a. A. lingualis ([Fig. 119], i; [Fig. 120], d).—The lingual artery leaves the external carotid near its beginning and passes craniomediad along the ventral border of the digastric muscle ([Fig. 120], 9), accompanied by the hypoglossal nerve. It gives off numerous small branches to the hyoid and pharyngeal muscles, then passes dorsad of the hyoglossus muscle ([Fig. 120], 6), where it gives off a branch which passes transversely across the middle line to communicate with the artery of the other side. Beneath the hyoglossus the artery turns craniad and passes into the tongue. Here it runs along the medial border of the styloglossus to the tip of the tongue, giving off numerous branches into the substance of this organ.