CHAPTER V 



THE CIRCULATION OF THE BLOOD 



THE blood is contained in a system of closed vessels through which it is 

 kept in circulation during the life of an individual. The energy to keep up 

 this motion is supplied by the heart, which is a large muscular organ con- 

 sisting of four great divisions, the right and left auricles and right and left 

 ventricles. The right ventricle discharges its blood into the pulmonary artery, 



FIG. 133. Diagram of the Circulation in an Animal with a Completely Separated Right 

 and Left Ventricle and a Double Circulation. (After Huxley.) Ad, Right auncle receiving the 

 superior and inferior venae cavae, Vcs and Vci; Dth, thoracic duct, the main trunk of the lymphatic 

 system; Ad, right auricle; Vd, right ventricle; Ap, pulmonary artery; P, lung; Vp, pulmonary 

 vein; As, left auricle; Vs, left ventricle; A o, aorta; D, intestine; L, liver; Vp, portal vein; Lv, 

 hepatic vein. 



through which it passes to the lungs, returning through the pulmonary veins to 

 the left auricle, and into the ventricle. From the left ventricle the blood fc 

 pumped into the great aorta, and through its branches distributed to the entire 

 body. The terminal arteries are continuous with the general capillaries of the 



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