186 THE HOUSE I LIVE IN. 



The heart has really four cavities in it, two 

 on the right side and two on the left. The 

 blood which has been sent out into all parts of 

 the body through the arteries, returns to the 

 first or upper part of the right side, and then 

 passes through into the right ventricle. As 

 soon as this ventricle is full, it contracts, and 

 presses its contents, the blood, into a great 

 artery, called the pulmonary artery, which 

 carries it to all parts of the lungs, whence it 

 comes back into the left side of the heart ; first 

 into the left auricle, and next into the left ven- 

 tricle. From the latter it is pressed, when 

 the heart contracts, into the great artery, or 

 aorta, and sent all over the body. 



These four smaller cavities or chambers, 

 taken together, hold, in an adult, about two or 

 three ounces of blood : or something more 

 than half a gill. The length of an adult heart, 

 measured on the outside, is about five inches. 

 We m,ay say, in general terms, that it is about 

 the size of a man's fist. 



A great deal more might be said about the 

 heart its cavities, structure, motion, situation, 

 &c., but 1 have said all that is necessary in 



