But, so far as
regards this particular topic, Aristotle, it must be confessed, has not
got very far beyond common knowledge. He knows a little about the
structure of the heart. I do not think that his knowledge is so
inaccurate as many people fancy, but it does not amount to much. A very
few years after his time, however, there was a Greek philosopher,
Erasistratus, who lived about three hundred years before Christ, and
who must have pursued anatomy with much care, for he made the important
discovery that there are membranous flaps, which are now called
"valves," at the origins of the great vessels; and that there are
certain other valves in the interior of the heart itself.
Fig. 1.--The apparatus of the circulation, as at present known. The
capillary vessels, which connect the arteries and veins, are omitted,
on account of their small size. The shading of the "venous system" is
given to all the vessels which contain venous blood; that of the
"arterial system" to all the vessels which contain arterial blood.
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