The Aorta, or great systemic artery of the body, consists of an arch, and descending portion; the latter is divided into the thoracic aorta, and the abdominal aorta. The arch may be exposed by the dissection already recommended for exhibiting the heart: it extends from the base of the left ventricle to the left side of the third dorsal vertebra. In this course its convexity is directed upwards, and its summit is on a level with the body of the second dorsal vertebra; its posterior extremity touches the spine, and in the adult subject its most prominent part is scarcely half an inch distant from the sternum. It is usually divided into three stages or portions, viz., an anterior, middle, and posterior.