CIRCULATION OF THE BLOOD. 93 



PART II. 

 CIRCULATION OF THE BLOOD AND NUTRITION. 



CHAPTER I. 



Apparatus of Circulation. Heart. Structure and Divisions. 

 Valves. Arteries. Aorta. Subclavian, carotid, facial arteries. 

 Branches in the lower limbs. 



202. THE chyle, or the nutritious part of the digested 

 food, is tarried from the digestive organs, in the abdomen, 

 through the absorbent mouths, and the lacteal tubes, and 

 great lacteal duct, to the great veins near the heart. There 

 it is mixed with, and becomes a part of, the blood. This 

 blood is to undergo certain changes in the lungs, and then 

 it is to be distributed to all the parts of the body. 



203. The apparatus for this distribution or circulation of 

 the blood consists of the heart, or central organ of motion ; 

 the arteries, which carry all the blood out of the heart to 

 the lungs and to the various parts of the body ; the capillary 

 vessels, in which nutrition takes place ; and the veins, which 

 carry the blood back to the heart. 



2.04. The heart (Fig. VII.) is a hollow, muscular organ, or 

 bag, composed of fibrous substance, like lean meat. It is 

 capable of contraction and expansion, like the muscular coat 

 of the stomach. When it contracts it diminishes its internal 

 cavity, and presses out the fluid contents or blood that is 

 within it. When it relaxes, its cavity is enlarged and allows 

 other fluid or blood to flow into it. 



205. The heart is placed in the centre of the chest, be- 

 tween the two lungs, (Fig. V. c.) Its larger end is upward, 



