142 



THE FEEDING OF ANIMALS 



these vessels the blood is mov- 

 ing in a constant stream, which 

 we call the circulation. It does 

 not move of itself, but is forced 

 along by a very powerful pump, 

 the heart. This is a highly 

 muscular organ divided into 

 four chambers, which are sepa- 

 rated by valves and partitions, 

 the two upper chambers being 

 called the right and left auri- 

 cles, and the two lower the right 

 and left ventricles. The right 

 auricle is above the right ventri- 

 cle and is separated from it by 

 a valve, and the same is true 

 of the left am-icle and ventricle. 

 (Fig. 7.) 



203. Circulation of bloody — 

 Out of the left ventricle the 

 blood is pumped into the arteries 

 and, after reaching the arterial 

 capillaries throughout the entire 

 body, it passes from these into 

 the smallest divisions of the 

 veins and comes back to the 

 heart along the venous system, 

 entering the right auricle. It 

 is then carried to the Ixmgs by 



Fig. 8. Diagram of circulation. 1, 

 heart; S, lungs; S, head and upper 

 extremities; 4i spleen; S, intestine; 6, 

 kidney; 7, lower extremities; S, liver. 

 (Collins.) 



