HEART AND BLOOD VESSELS 



201 



J*> 



ute. It is obvious, therefore, 

 that the work which the heart 

 does is very great. 1 



The heart is located in the 

 thoracic, or chest cavity, a little 

 to the left side and between the 

 lungs. It is a cone-shaped organ, 

 inclosed in a membranous bag" 

 called pericardium (per-i-car'di- 

 um : Greek, peri 



U around ; cardia, 



heart). 



The heart is 

 divided by a wall 

 into right and left 



chambers. A nearly complete cross parti- 

 tion divides each side into upper chambers, 

 the auricles, and the lower ones, the ventri- 

 cles. The opening between an auricle and 

 a ventricle is guarded by a valve, which is 

 partly membranous and partly muscular. 

 The auricles receive blood from the veins, 

 while the ventricles force blood into the 

 arteries. 

 Artery is the name given to the blood vessels which 

 carry blood from the heart, and vein is the term applied 



Figure 214. — Heart. 



Figure 215 

 Diagram 

 Vein. 



of 



Showing the 

 valves. 



1 " The work the heart does during the day is about equal to the energy 

 expended by man in climbing to the top of a mountain 3600 feet high. 

 Assuming that the man weighs about 150 pounds, this would be equal to 

 an amount of energy sufficient to lift 00 tons to a height of three feet 

 The work of the left side is greater than that of the right, since the 

 former has to drive the blood all over the body, while the latter baa only 

 to force it to the lungs which are near by. For this reason the muscle 

 walls of the right ventricle are much thinner than those of the left 

 ventricle." — Conn and Buddington. 



