353. The ventricles contract quicker and more forcibly than the auricles, and they are three times longer in dilating than contracting. The walls of the right ventricle, being thinner than the left, are more distensible, and thus this cavity will contain a greater amount of blood. This arrangement adapts it to the venous system, which is more capacious than the arterial. The thicker and more powerful walls of the left ventricle adapt it to expel the blood to a greater distance. 354. The valves in the heart permit the blood to flow from the auricles to the ventricles, but prevent its reflowing. The valves at the commencement of the aorta and pulmonary artery, permit the blood to flow from the ventricles into these vessels, but prevent its returning. -=-=-=-=-=-=-=-=-=-=-=-= 352-366. _Give the physiology of the circulatory organs._ 352. What do the contraction and relaxation of the muscular walls of the heart produce? How do the auricles and ventricles contract and dilate? 353. What is said of the contraction and dilatation of the ventricles in the heart? How is the right ventricle adapted to its function? How the left? 354. What is the use of the valves in the heart? Those of the aorta and pulmonary artery? -=-=-=-=-=-=-=-=-=-=-=-= 355. The function of the different parts of the heart will be given, by aid of fig. 74. The blood passes from the right auricle (3) into the right ventricle, (5,) and the tricuspid valves (6) prevent its reflux; from the right ventricle the blood is forced into the pulmonary artery, (7,) through which it passes to the lungs. The semilunar valves (9) prevent this circulating fluid returning to the ventricle. The blood, while passing over the air-cells in the lungs, in the minute divisions of the pulmonary artery, is changed from a bluish color to a bright red. It is then returned to the left auricle of the heart by the pulmonary veins, (11, 11.) [Illustration: Fig. 74. 1, The descending vena cava, (vein.) 2, The ascending vena cava, (vein.) 3, The right auricle. 4, The opening between the right auricle and the right ventricle. 5, The right ventricle. 6, The tricuspid valves. 7, The pulmonary artery. 8, 8, The branches of the pulmonary artery that pass to the right and left lung. 9, The semilunar valves of the pulmonary artery. 10, The septum between the two ventricles of the heart. 11, 11, The pulmonary veins. 12, The left auricle. 13, The opening between the left auricle and ventricle. 14, The left ventricle. 15, The mitral valves. 16, 16, The aorta. 17, The semilunar valves of the aorta.] -=-=-=-=-=-=-=-=-=-=-=-= 355. Describe the course of the blood from the right auricle in the heart to the lungs. -=-=-=-=-=-=-=-=-=-=-=-=