This vessel, the smaller of the divisions of the common aorta, is about 2 to 2 1/2 inches in length. On leaving its parent trunk it passes in a forward direction beneath the trachea or windpipe, and soon divides into two unequal branches, one passing to the right and the other to the left. The right one is the arteria innominata, and the left one the axillary artery. The right branch is much the larger of the two, for in addition to giving blood to the fore-limb and the anterior part of the trunk, like its fellow, it also supplies the head by means of a large branch, the cephalic artery. Each of these vessels, on leaving the anterior aorta, gives off eight branches of considerable size, as follows: -

1. Dorsal.

2. Superior Cervical.

3. Vertebral.

4. Internal Thoracic.

5. External Thoracic.

6. Inferior Cervical.

7. Supra-scapular.

8. Subscapular.

These vessels divide and subdivide in their course, and furnish blood to the withers, the neck, the shoulders, and the walls of the chest. The vertebral artery requires special notice, inasmuch as it courses along the neck, partly enclosed in small bony canals in the transverse processes of the six anterior cervical vertebrae. In its course it supplies many branches to the deep cervical muscles, and others which enter the spinal canal and are distributed to the spinal cord.

After giving off the arteries above-named, the axillary descends along the inner aspect of the upper arm, where it takes the name of the brachial or humeral artery.

The Anterior Aorta And Its Branches.

The Anterior Aorta And Its Branches.