Aor'ta, the great artery, the trunk of the arterial system. It rises from the left ventricle of the heart toward the top of the breast-bone; then makes a curve, called the arch of the aorta, whence it gives off branches to the head and upper extremities; then going downward through the chest, it gives off branches to the trunk, thence it passes through the diaphragm and finally divides into the two iliacs, which supply the pelvis and lower extremities. See ARTERIES; CIRCULATION; HEART.