CHAPTER XIV. 

 THE ANATOMY OF THE CIRCULATORY ORGANS. 



The Organs of Circulation are the heart and the blood- 

 vessels; the blood-vessels are of three kinds, arteries, capil- 

 laries, and veins. The arteries carry blood from the heart 

 to the capillaries; the veins collect it from the capillaries 

 and return it to the heart. There are two distinct sets of 

 blood-vessels in the body, both connected witlT^he heart; 

 one set carries blood to, through, and from the lungs, the 

 other guides its flow through all the remaining organs; the 

 former are known as the pulmonary, the latter as the sys- 

 temic blood-vessels. 



General Statement. During life the pumping of the 

 heart keeps the blood flowing rapidly through the paths 

 marked out for it by the blood-vessels ; these paths it never 

 leaves except in cases of disease or injury. 



The blood-vessels form a continuous system of closed 

 tubes comparable in a certain way to the water-mains of a 

 city. These tubes begin at the heart, and are very much 

 branched except close to it, just as the water pipes are 

 single only where the main aqueduct leaves the reservoir, 



Name the organs of circulation. Name the kinds of blood-ves- 

 sels. What is the function of the arteries? Of the veins? How 

 many sets of blood-vessels are there in the body? What does each 

 set do? What are they called? 



What is brought about by the beat of the heart? Under what 

 circumstances may blood leave a blood channel? 



What do the blood-vessels form? Illustrate their function by 

 comparison with the water-mains of a city. 



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