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Life and Health 



however, include a set of valves which open like folding 



doors between the two rooms. 



The heart thus has four cavities, two on each side. The 



two upper are called auricles, from the resemblance of one 



corner of each to the ear of a 

 dog. The two lower cavities 

 are called ventricles. 

 4 215. The Valves of the 

 Heart. The valves of the heart 

 consist of thin, but strong, 

 triangular folds of connective 

 tissue which hang down from 

 the edges of the passages into 

 the ventricles. They may be 

 compared to swinging doors 

 which, by opening only one 

 way, allow the blood to flow 

 from the auricles to the ven- 

 tricles, but by instantly fold- 

 ing back prevent its return. 



The valve on the right side 

 is called the tricuspid, because 

 it consists of three little folds 

 which fall over the opening 

 and close it. It is kept from 

 falling too far by a number of 

 slender threads called chordae 

 tendineae. 



The valve on the left side, 

 called the mitral, from its 



fancied resemblance to a bishop's miter, consists of two 



folds which close together as do those of the tricuspid 



valve. 



FIG. 71. Right Cavities of 

 the Heart. 



A, aorta ; B, superior vena cava ; C, C, 

 right pulmonary veins ; D, inferior 

 vena cava; , section of coronary 

 vein; F, right ventricular cavity; 

 H, posterior curtain of the tricuspid 

 valve; K, right auricular cavity; 

 Af, fossa ovalis, oval depression, par- 

 tition between the auricles formed 

 after birth. 



