Aorta
2 of the 6 encyclopedias on this shelf carry an entry for Aorta. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
the great artery through which the heart forces blood to the entire body. In the human body it springs from the left ventricle, and arches backward to the spinal column, thence downward. From the very beginning the aorta begins to give off small arteries; first, those that supply the heart itself, then from the top of the arch, the arteries that supply the head, neck, and arms. On its downward descent the aorta gives off branches that supply the body with arterial blood, dividing finally into two large arteries, one for each leg. All arteries save that which carries blood to the lungs for purification are branches of the aorta. The aorta of an average person is about half an inch in diameter. It is considered that all the blood of the body is pumped through the aorta on an average once each twenty-three minutes. See Heart ; Blood
Collier's New Encyclopedia (1921)
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 downforms the arch of the aorta. Conward tinuing 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.
What Has Changed in the Last Century
The anatomy in both accounts still stands: Collier's 1921 description of the ascending aorta, arch, descending and abdominal segments, the bifurcation into the iliac arteries at the fourth lumbar vertebra, and the three semilunar valves is exactly what medical students learn today. Two of Aiton's 1910 figures do not survive: an adult aorta measures roughly 3 cm across at the root rather than "about half an inch," and with a resting cardiac output near five litres a minute the whole blood volume passes through it about once a minute, not once in twenty-three. What has truly changed is that the aorta became operable. Michael DeBakey and others were replacing diseased segments with Dacron tubes by the 1950s, Juan Parodi reported the first endovascular stent-graft repair of an abdominal aneurysm in 1991, and since 2002 a diseased aortic valve can be replaced through a catheter without opening the chest.
Written for this edition, 2026.