. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 639 blood which has served the purposes of nu- trition, and the other uses for which the blood is destined throughout the body, on being re- turned to the heart, is directed by the cavities on the right side of that organ to the lungs, and made to pass through them before returning to the left side of the heart to repeat its course through the nutritive vessels of the body. In all those animals in which there exists a disposition of the heart and bloodvessels such as that described, the circulation is said t
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CIRCULATION. 639 blood which has served the purposes of nu- trition, and the other uses for which the blood is destined throughout the body, on being re- turned to the heart, is directed by the cavities on the right side of that organ to the lungs, and made to pass through them before returning to the left side of the heart to repeat its course through the nutritive vessels of the body. In all those animals in which there exists a disposition of the heart and bloodvessels such as that described, the circulation is said to be double, because the blood is moved in two circles at once, and the respiration is said to be complete, because the whole of that blood which has passed through the nutritive vessels of the body is subjected to the respiratory action of air in the lungs. The blood returned from the lungs of a bright red colour, or arterial blood, on being expelled from the left ventricle (jig. 312, H) Fig. 312.*. Circulation in Man. * In all the figures relating to the circulation in different animals the same letters indicate corres- ponding parts as follows : H, the heart or the common ventricle ; h, the common auricle ; At the aorta or trunk of the systemic arteries ; a, its branches ; a*, the carotids. V, the great systemic veins or vena cava infe- rior ; w, its branches; t>*, the vena cava superior ; c, the capillary vessels ; P, the pulmonary artery; p, the pulmonary vein ; B, the branchial artery; b, the branchial vein ; D, the ductus arteriosus ; d, ductus venosus ; /, foramen ovale; U, umbilical arteries ; u, umbilical vein ; by the muscular contraction of that cavity, passes into the aorta or great artery of the system (A), and is distributed in various pro- portions to all parts of the body by the branches of the aortic trunk («) and their in- finitely minute ramifications. The smallest arteries lead, by an intermediate set of minute tubes to which the name of capillary vess
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