CHAPTER V. 



THE CIRCULATION OF THE BLOOD. 



THE Heart is a hollow muscular organ containing four chambers, two 

 auricles and two ventricles, arranged in pairs. On each side (right and 

 left) of the heart is an auricle joined to and communicating with a ven- 

 tricle, but the chambers on the right side do not directly communicate 

 with those on the left side. The circulation of the blood is chiefly 



FIG. 90. Diagram of the Circulation. 



carried on by the contraction of the muscular walls of these chambers of 

 the heart, the auricles contracting simultaneously, and their contraction 

 being followed by the simultaneous contraction of the ventricles. The 

 blood is conveyed away from the left side of the heart by the arteries, 

 and returned to the right side of the heart by the veins, the arteries and 

 veins being continuous with each other at one end by means of the heart, 

 and at the other by a fine network of vessels called the capillaries. The 



