THE CIRCULATION 



45 



Connection with Arteries and Veins. Though the heart 

 is in communication with all parts of the circulatory system, 

 it makes actual connection with only 

 a few of the blood tubes. These 

 enter the heart at its upper portion 

 (Fig. 15), but connect with its differ- 

 ent cavities as follows : 



1. With the right auricle, the 

 superior and the inferior venae cavae 

 and the coronary veins. The supe- 

 rior vena cava receives blood from 

 the head and the upper extremities ; 

 the inferior vena cava, from the 

 trunk and the lower extremities ; 

 and the coronary veins, from the 

 heart itself. 



2. With the left auricle, the four 

 pulmonary veins. These receive 

 blood from the lungs and empty it 

 into the left auricle. 



3. With the right ventricle, the the circ lation ' . 



in general the work done 



pulmonary artery. This receives by each part of the heart, 

 blood from the heart and by its The r 'g bt ventricle forces 



i , ,. . M .. ,, the blood through the 



branches distributes it to all parts lungs and into g kft 



Of the lungs. auricle. The left ventricle 



4. With the left ventricle, the aorta. forces blood *h rou g h all 



, . parts of the body and back 



The aorta receives blood from the to the right auricle> The 

 heart and through its branches de- auricles force blood into 

 livers it to all parts of the body. the ventricles - 



How the Heart does its Work. The heart is a muscular 

 pump 1 and does its work through the contracting and 



FIG. 17. Diagram of 



1 The heart at first glance seems to bear little resemblance to the pumps in 

 common use. When it is remembered, however, that any contrivance which 



