Aorta
the largest artery in the human body, and the main trunk of the arterial system itself. It takes its departure from the upper part of the left ventricle of the heart, whence it runs upward and to the right, at that part of its progress being called the ascending aorta; then it turns to the left, passes the spinal column, and bending downward forms the arch of the aorta. Continuing its course along the left of the spine, it is called the descending aorta.
Passing through the aperture in the diaphragm into the abdomen, it becomes the abdominal aorta. Finally, it bifurcates about the fourth pair of lumbar vertebræ, and forms the two primitive iliac arteries. Upward from the heart the ramifications are numerous and exceedingly important. The aorta has three valves called the sigmoid or semi-lunar valves, to prevent the reflux of the blood into the heart.
AOSTA (a-os'ta), a cathedral city of Italy, on the Dora Baltea, 19 miles from the opening of the great St. Bernard Pass, and 80 miles N. N. W. of Turin by rail. It is surrounded by rich or- APE chards, vineyards, and almond plantations. It is the ancient Augusta Prætoria; and several monuments of the Roman times still remain. St. Bernard was Archdeacon of Aosta; and here Anselm, Archbishop of Canterbury, was born. Near by are the celebrated baths and mines of St. Didier. The beautiful valley of Aosta is rich in woods, pastures, minerals, and mineral walls. French is generally spoken. Pop. about 7,000.