CIRCULATION OF 



96 



Fm. VIE. Heart laid open. View of the four Chambers of 

 the Heart. 



a. Left ventricle. 



b Right ventricle. 



r Partition wall between the 

 two sides. 



?. Right auricle. 



e. Left auricle. 



/, g. Partitions between the au- 

 ricles and ventricles. 



h, h. Great artery leading from 

 the left ventricle to the whole 

 body. 



i, i. Great vein carrying the 

 blood to the heart from the whole 

 body. 



k, k. Arteries leading to the 

 lungs. 



I, i. Veins leading from the lungs 



The arrows show the course of the blood through the heart. 



207. Each of the two grand divisions of the heart is again 

 divided into two smaller chambers. On the left side, the 

 one above (Fig. VIII. e) is called the left auricle, and the 

 one below, (Fig. VIII. a,) the left ventricle. On the right 

 side, the chamber above (Fig. VIII. d) is called the right au- 

 ricle, and the one below, (Fig. VIII. b,) the right ventricle. 

 These make four separate chambers in the heart. There is 

 no communication between the two auricles, nor any between 

 the two ventricles ; but there is a passage-way on each side, 

 opening from the auricle above to the ventricle below, 

 through which the blood passes from the upper to the lower 

 chamber. 



208. The blood flows from the auricle to ths ventricle, but 

 not backward from the ventricle to the auricle. There are 

 valves placed at these passage-ways in the heart, which open 

 to allow the blood to pass downward, but they close, and 

 prevent its passing upward. These valves act on the principle 

 of the valve in the common pump box, which opens when the 

 water below presses upward, and allows it to pass through ; 



