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When men saw both the pulmonary artery and the pulmonary veins losing themselves in the lungs, of course it became a puzzle to them to know how or by what means the right ventricle should distribute the blood to the body, or the left draw it from the venae cavae.
From the liver extend the venae cavae, one to supply the head and arms, the other the lower extremities: extending from the right heart was a branch, corresponding to the pulmonary artery, the arterial vein which distributed blood to the lungs. This was the closed venous system. Warmed in the ventricle, it distributed vital heat to all parts of the body.
Two pairs of valves are situate in the external jugular, and another pair in the internal jugular, but they do not prevent regurgitation of blood upward. An anomaly exists in the absence of valves from parts where they are most needed, such as the venae cavae, the spinal, iliac, haemorrhoidal, and portal veins.
In despite of the care that was taken of them, they died on the second day. Incisions were made through the skin, but in opening them no blood flowed. The venae cavae themselves did not contain any there were only two clots of blood in the cavities of their hearts.
When the valves are raised and brought together, they form a three-cornered line, such as is left by the bite of a leech; and the more they are forced, the more firmly do they oppose the passage of the blood. The tricuspid valves are placed, like gate-keepers, at the entrance into the ventricles from the venae cavae and pulmonary veins, lest the blood when most forcibly impelled should flow back.
The right ventricle, in its turn being overworked, becomes dilated, and as a result of the inability of the right ventricle to evacuate its contents perfectly, the right auricle is unable to force its venous blood into the right ventricle, and there is then a damming back and sluggish circulation in the superior and inferior venae cavae.
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