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).

[Fig. 119].—Common Carotid Artery and Internal Jugular Vein.