110 



THE CIRCULATION. 



fancied resemblance to the ear of a dog, and two at the 

 apex or point, called ventricles. An auricle and a ventricle 



on the same side, 

 communicate with 

 each other, but there 

 is no opening from 

 side to side. It is 

 customary to regard 

 the heart as a double 

 organ, and to speak 

 of its division into 

 the right and left 

 heart. For while 

 both halves act to- 

 gether in point of 

 time, each half sus- 

 tains an entirely dis- 

 tinct portion of the 

 labor of the circu- 

 lation. Thus, the 

 right heart always 

 carries the dark or 

 venous blood, and the left always circulates the bright or 

 arterial blood. 



20. If we examine the heart, we at once notice that 

 though its various chambers have about the same capacity, 

 the walls of the ventricles are thicker and stronger than 

 those of the auricles. This is a wise provision, for it is by 

 the powerful action of the former that the blood is forced 

 to the most remote regions of the body. The auricles, on 

 the contrary, need much less power, for they simply dis- 

 charge their contents into the cavities of the heart near at 

 hand and below them into the ventricles. 



FIG. 29. SECTION OP THE HEART. 



A, Right Ventricle 



B, Left " 



C, Right Auricle. 



D, Left Auricle. 



E, F, Inlets to the Ventricles. 

 G, Pulmonary Artery. 

 H, Aorta. 



20. Capacity of the chambers of the heart ? What wise provision is men- 

 tioned ? The auricles ? 



