164 



CIRCULATION OF THE BLOOD. 



Fig. 31. 

 A view of the heart, showing its resemblance to a fire engine. 

 C 



B, A, C, D, the four rooms in the heart, b, a, c, d, four principal 

 veins and arteries conveying the blood to and from the heart, 

 — (the dotted lines representing the course.) 



b t a vein bringing the blood from the body into B, the first receiv- 

 ing room, called the right auricle; whence it passes into A. 

 the first forcing room, termed the right ventricle.— A small 

 valve is represented playing over the orifice, and opening into 

 the forcing room, to prevent the return of the blood, exactly 

 as in the fire engine, a, the artery by which the blood is 

 thrown into the lungs, e, the valve opening into this artery, 

 and preventing the return of the blood, the same as in the en- 

 gine. 



— Again — 



c, a vein by which the blood is returned from the lungs, and de- 

 livered into C, the second receiving room, called the left au- 

 ricle ; whence it passes into D, the second forcing room, term- 

 ed the left ventricle ; and hence into d, the great artery which 

 distributes it over the body. The valves — the same as in the 

 other rooms. 



N. B. The situations, shapes and dimensions of the different 

 parts are not exactly observed in the figure. In the heart, the 

 auricles B, C, have more than one vein. The valves are also 

 differently shaped from those in the figure. But the leading 

 principles are seen ; sufficient to show that, in construction, 

 the heart is literally a double fire engine. 



