aorta

[In Fr. aorte; Sp. & Port. aorta; Gr. ἀορτή (aorte) = (1) In pl., the lower extremities of the windpipe; (2) later & sing., the aorta (see def.). From ἀείρω ( αείτō ) = to lift.] 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 progre being called the ascending aorta; then it turns to the left, pa es the spinal column, and bending downwards forms the arch of the aorta. Continuing its course along to the left of the spine, it is called the descending aorta. Pa ing 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. Upwards 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.