'auricles'--as any part of the heart at all; but when they spoke of the
heart they meant the left and the right ventricles; and they described
those great vessels, which we now call the 'pulmonary veins' and the
'vena cava', as opening directly into the heart itself.

What Erasistratus made out was that, at the roots of the aorta and the
pulmonary artery (Fig. 1) there were valves, which opened in the
direction indicated by the arrows; and, on the other hand, that at the
junction of what he called the veins with the heart there were other
valves, which also opened again in the direction indicated by the
arrows. This was a very capital discovery, because it proved that if
the heart was full of fluid, and if there were any means of causing
that fluid in the ventricles to move, then the fluid could move only in
one direction; for you will observe that, as soon as the fluid is
compressed, the two valves between the ventricles and the veins will be
shut, and the fluid will be obliged to move into the arteries; and, if
it tries to get back from them into the heart, it is prevented from
doing so by the valves at the origin of the arteries, which we now call
the semilunar valves (half-moon shaped valves); so that it is
impossible, if the fluid move at all, that it should move in any other
way than from the great veins into the arteries. Now that was a very
remarkable and striking discovery.

But it is not given to any man to be altogether right (that is a
reflection which it is very desirable for every man who has had the
good luck to be nearly right once, always to bear in mind); and
Erasistratus, while he made this capital and important discovery, made a
very capital and important error in another direction, although it was
a very natural error. If, in any animal which is recently killed, you
open one of those pulsating trunks which I referred to a short time