Circulation

(sür-ku-lā'shun.) [FromL. circulor, to go round.] (Anat.) The natural motion of the blood in a living animal, by which it proceeds from the heart to all parts of the body by the arteries, and returns to the heart by the veins. (See Figs. 45 and 181). The circulation of the blood is performed in the following manner: It is returned to the right auricle of the heart by the descending and ascending vena cava, which, when distended, contracts and sends it into the right ventricle; from the right ventricle it is propelled through the pulmonary artery, to circulate through and undergo a change in the lungs, being prevented from returning into the right auricle by the closing of valves. Having undergone this change in the lungs, it is brought to the left auricle of the heart by the four pulmonary veinsς, and thence is evacuated into the left ventricle. The left ventricle, after having been distended, contracts, and throws the blood through the aorta to every part of the body, by the arteries, to be returned by the veins 4 32 23 4 5-5 6 6 13-14 14 7 7 -10 159 8 16 11 7 12 Fig. 181. - LUNGS AND HEART. 1. Trachea; 2, 2, carotid arteries; 3, 3, jugular veins; 4, 4, subclavian arteries; 5, 5, veins from the right and left arms; 6, 6, lungs; 7, 7, 7, aorta: 8, right auricle; 10, left auricle; 11, right ventricle; 9, left ventricle; 12, heart; 13, pulmonary artery; 14, pulmonary veins; 15, vena cava sup.; 16, venacava inf. into the venacava. It is prevented from pa ing back from the left ventricle into the auricle by a valvular apparatus; and the beginning of the pulmonary artery and aorta is also furnished with similar organs, which prevent its returning into the ventricles. Seo ARTERY, HEART, . [s. 190]