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A distended or enlarged vein. Pertaining to or possessing blood or lymph vessels. Causing motion to the vessels. Vaso-motor nerves cause contraction and relaxation of the blood-vessels. Venæ Cavæ, pl. of Vena Cava. "Hollow veins." A name given to the two great veins of the body which meet at the right auricle of the heart Pertaining to, or contained within, a vein. Ventilation.
It is now well to study the circulation as a whole, tracing the course of the blood from a certain point until it returns to the same point. We may conveniently begin with the portion of blood contained at any moment in the right auricle. The superior and inferior venæ cavæ are busily filling the auricle with dark, impure blood. When it is full, it contracts.
With the lady in question this portion proved to be the mouth. Commencing at the right ear, it swept with a terrific chasm to the left the short pendants which she wore in either auricle continually bobbing into the aperture.
The disturbed circulation is evidenced by imperfect peripheral circulation and capillary sluggishly, with at times pendent edema of the feet and ankles, but, perhaps, little congestion of the lungs. The left ventricle being sufficient, there is no damming back through the left auricle to the lungs.
When this is full, the muscles in the wall of the ventricle contract, the valve flaps fly up, and the blood is squirted out through the pulmonary artery to the lungs. Here it passes through the capillaries round the air cells, loses its carbon dioxid, takes in oxygen, and is gathered up and returned through great return pipes to the receiving chamber, or auricle, of the left side of the heart.
But this blood, instead of flowing directly to the heart, is passed through the portal vein to the liver, where it enters a second set of capillaries and is brought very near the liver cells. From the liver it is passed through the hepatic veins into the inferior vena cava, and by these it is emptied into the right auricle.
Subsequently it is shortened and widened, and becomes divided by a contraction into two parts, a ventricle and an auricle; it is now the heart of a fish. A subdivision of the auricle afterwards makes a triple-chambered form, as in the heart of the reptile tribes; lastly, the ventricle being also subdivided, it becomes a full mammal heart.
As soon as the left ventricle is full, it contracts. The mitral valve instantly closes and blocks the passage backward into the auricle; the blood, having no other way open, is forced through the semilunar valves into the aorta. Now red in color from its fresh oxygen, and laden with nutritive materials, it is distributed by the arteries to the various tissues of the body.
Make an incision in the left auricle. Examine its inner surface and find the places of entrance of the pulmonary veins. Examine the mitral valve from above. Compare the two sides of the heart, part for part.
By the former the blood passes from the right ventricle through the lungs, and is then returned to the left auricle; by the latter it passes from the left ventricle through all parts of the body, returning to the right auricle.
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