Part 66

The right branch passes under (dorsocaudad of) the aortic arch, and reaches the right lung at about the junction of the cranial lobe with the remainder of the lung. The cranial lobe of the right lung is therefore said to be =eparterial=, since it is craniad of the pulmonary artery; the other lobes are hyparterial. The right branch divides at its entrance to the lung and is distributed to its lobes.

2. =Aorta= (Fig. 115, g; Fig. 118, a).

The aorta is the single great vessel which conveys blood from the left ventricle. It makes a sharp semicircular curve dorsad (Fig. 118, a′) and to the left, passes caudad at the left side of the vertebral column, and passes between the crura of the diaphragm to reach the abdominal cavity. It is divisible into =thoracic aorta= (Fig. 118) and =abdominal aorta= (Fig. 126).

A. =Thoracic Aorta= (Fig. 118).--The first portion of the thoracic aorta, curved as above described, is the =aortic arch= (a′). It lies in the thoracic cavity opposite the interval between the third and fourth or fourth and fifth ribs. It is separated from the vertebral column on the right by the superior vena cava (q), and on the left by the œsophagus (4). At its beginning it lies a little to the right of the median plane; but it passes at once to the left side of the vertebral column.

BRANCHES OF THE THORACIC AORTA.

1. =Aa. coronariæ.=--The coronary arteries are two. They arise from the aortic sinuses. The left one (Fig. 118, p) leaves the aorta on the left side, passes dorsad of the pulmonary artery, and divides into two branches, one of which follows the auriculoventricular groove (sulcus coronarius) to the dorsal side of the heart and sends branches to the adjacent heart-walls, while the other runs onto the ventricles, following approximately the ventral border of the ventricular septum. The right coronary artery passes in the auriculoventricular groove toward the right and dorsad, and supplies the adjacent walls of the heart.

2. =A. anonyma= (Fig. 115, j; Fig. 118, b).--The innominate artery passes craniad from the convexity of the aortic arch (a′). It gives rise first to a small =mediastinal artery= (m) which passes ventrad into the mediastinum, then to the =left common carotid= (Fig. 115, l), then to the =right common carotid= (Fig. 115, m). Sometimes the carotids are given off from a common trunk. Beyond the right common carotid the innominate is continued as the =right subclavian= (Fig. 115, n).

a, aorta (a′, aortic arch); b, innominate artery; c, left subclavian; d, right subclavian; e, right common carotid; f, left common carotid; g, costocervical axis; g′, vertebral artery; h, internal mammary artery; i, axillary artery; j, thyrocervical axis; k, A. transversa scapulæ; m, mediastinal artery; n, intercostal arteries; o, œsophageal arteries; p, left coronary artery; q, superior vena cava; r, internal mammary vein; s, the two innominate veins; t, sternal artery; u, costocervical vein; v, vertebral vein; w, axillary vein; x, vein to clavotrapezius and lateral ends of the pectoral muscles; y, vein accompanying second branch of A. transversa scapulæ; z, thyrocervical vein. 1, external jugular vein; 2, internal jugular vein; 3, vena cordis magna; 4, œsophagus; 5, thoracic duct; 6, one of the lymphatic ducts from the neck. I, first rib (cut); VIII, eighth rib (cut); XII, twelfth rib (cut).]

3. =A. subclavia sinistra= (Fig. 115, k; Fig. 118, c).--The left subclavian passes craniad from the convexity of the aortic arch. It curves about the first rib (Fig. 118, I) to enter the armpit, where it becomes the =axillary artery= (i).

4. =Aa. intercostales= (n).--The intercostal arteries are given off from the dorsal side of the aorta. Each passes to an intercostal space and divides into three branches. One of these passes ventrad along the caudal margin of the cranial one of the two ribs between which it extends. Another goes to the deep muscles of the back, and the third enters the spinal canal through the intervertebral foramen. The arteries for the first and second (and sometimes the third) intercostal space usually arise from the subclavian (costocervical axis, Fig. 118, g).

5. =Aa. bronchiales.=--The bronchial arteries are two, and arise either from the aorta opposite the fourth intercostal space or from the fourth intercostal arteries. They accompany the bronchi to the lungs.

6. =Aa. œsophageæ= (Fig. 118, o).--The œsophageal arteries are small branches of varying origin passing to the œsophagus.

7. =Aa. lumbales.=--The lumbar arteries correspond to the intercostals, but pass off between the lumbar vertebræ. The obliquity of the diaphragm throws the origin of one or two pairs of them within the thorax.

A. CAROTIS COMMUNIS. THE COMMON CAROTID ARTERY. (Fig. 115, l and m; Fig. 119, a).

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).

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.

b. =Rami musculares.=--Muscular branches pass to the digastric and to the hyoid muscles. A small branch (Fig. 119, h), which may arise either from the external carotid or from the common carotid near the beginning of the external carotid, passes to the larynx and supplies the thyroarytenoid and lateral cricoarytenoid muscles of the larynx.

c. =A. maxillaris externa= (Fig. 119, j).--The external maxillary artery leaves the external carotid (m) opposite the angle of the jaw and at about the dorsal border of the digastric muscle (8). It passes craniad, lying at first beneath the digastric muscle and sending a branch to the submaxillary gland. Opposite the caudal border of the mylohyoid muscle it gives off the =submental= artery, turns dorsad, emerges from beneath the digastric, and passes along the cranial border of the masseter onto the face. Here it divides into =superior= (k) and =inferior= (l) =labial= branches, which pass along the upper and lower lips, respectively, giving off numerous branches.

The =submental= artery passes to the symphysis menti between the digastric and mylohyoid muscles, giving off on its course collateral branches to the muscles of this region.