The Blood and its Circulation 



The Semilunar Valves. From the right ventricle 

 a large vessel, called the pulmonary artery, passes to the 

 lungs, and from the left ventricle a large vessel, called the 

 aorta, arches out to the general 

 circulation of the body. The 

 openings from the ventricles 

 into these vessels are guarded 

 by the semilunar valves. Each 

 valve has three folds, each half- 

 moon shaped, hence the name 

 " semilunar." These valves, 

 when shut, prevent any back- 

 ward flow of the blood from 

 the pulmonary artery to the 

 right ventricle, and from the 

 aorta to the left ventricle. 

 Y. 217. The Great Blood Vessels 

 connected with the Right Side 

 of the Heart. There are a few 

 large blood vessels connected 

 with the heart, the relative 

 position and the use of which 

 must be understood. 



The two largest veins in the 

 body, the superior vena cava and 

 the inferior vena cava, open into 

 the right auricle. They bring 

 venous blood from all parts of 

 the body and pour it into the right auricle. 



From the right ventricle arises one large vessel, the pul- 

 monary artery, which soon divides into two branches of 

 nearly equal size, one for the right lung, the other for 

 the left. 



FIG. 72. Left Cavities of 



the Heart. 



, , right pulmonary veins ; with S, 

 openings of the veins; , D, C, 

 aortic valves; fi, aorta; P, pulmo- 

 nary artery; O, pulmonic valves; 

 H, mitral valve ; K, columnae car- 

 nceae ; M, right ventricular cavity ; 

 N, interventricular septum. 



