THE CIKCULATIOX. 



733 



TIG. 022. Theoretical plan of the circulatory system. 



H, D, C, E. The canal for red blood; E, B, A, G. Canal 

 for black blood. The arrows indicate the course of the 

 blood. The two canals arc represented in then* middle por- 

 tion, A B, C D, as isolated; but in nature they are envel- 

 oped at this point in a common sac that concurs to form 

 the heart. 



through the veins which finally end in the vena 

 cava b, and enters the right auricle c. From 

 this it is pumped into the right ventricle d, 

 which, contracting in its turn, forces it on into 

 the pulmonary artery e, spreading out upon 

 the lining membrane of the lungs, to form the 

 capillaries of that organ at /, from which it is 

 returned to the left auricle g through the pul- 

 monary veins. From the left auricle it is 

 driven on through the left ventricle; and this, 

 by its powerful contraction, forces the blood 

 through the aorta i, and the arteries of the 

 whole body to the capillaries a, from which the 

 description commenced. 



While the venus blood is on its way to the 

 heart, when near it, it is met by the thoracic 

 duct (see k, y, Fig. 626, and k, Fig. 627), 

 which conveys into this returning blood the 

 nutritive property of the food extracted from 

 it by the digestive organs. With this new 



FIG. 623. Plan of the 

 circulation. 



A. Capillaries on the gen- 

 eral surf ace; B. Vena cava; 

 C. Right auricle ; D. Right 

 ventricle ; E. Pulmonary 

 artery; F. Capillaries of the 

 lungs, uniting to form the 

 pulmonary veins, which en- 

 ter G. The left auricle; II. 

 The left ventricle; I. The 

 aorta posteria, dividing into 

 smaller arteries, and united 

 with the capillaries at A; J. 

 Trunk of the aorta anterior. 



