THE HEART 



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283. Cavities of the heart. The heart is designed to 

 pump two separate streams of blood at once. Its left side 

 pumps blood through the 

 whole body, while its right 

 side pumps it only through 

 the lungs. The cavity on 

 each side is partly divided 

 into an upper chamber called 

 an auricle, and a lower one 

 called a ventricle. Each 

 auricle has thin, flabby walls, 

 and does little of the work of 

 pumping blood. 



The ventricles have thick 

 and strong walls, which form 

 nearly all the bulk of the 

 heart. The left ventricle has 

 walls three times as thick as Valves of the heart - 



the right Ventricle, for it must a artery with its lower end split open. 



pump blood through a much 

 greater part of the body. 

 From each ventricle a tube, 

 called an artery, conducts the 

 blood away. 



\ 284. Valves of the heart. 

 Blood enters each auricle 

 through tubes called veins, 

 and streams through the 

 opening into the ventricle, 

 but is prevented from flow- 



vein leading into the heart. 

 c auricle with the front cut away. 

 d cut edge of the auricle, showing its 



thinness. 

 e semilunar valves; their upper edges 



are free and movable. 

 / mitral valve spread open. 

 g strings from the edge of the curtain 



of the valve to steady it. 

 h muscular projection upon the inside 



of the ventricle to which the strings 



are attached. 

 i indentations upon the inner surface of 



the ventricle. 



/ wall of the ventricle, showing its thick- 

 ness as compared with that of the 



auricle, d. 



ing back by thin, strong cur- 

 tains which are attached to the edge of the opening and 

 hang suspended in the ventricle. From the edges of each 



