EEPTULES. 



189 



155 - 



circulation in Mammals 

 and Birds, is taken from 

 my First Book in Phys- 

 iology. In this figure, in 

 which the shaded part 

 shows where the blood 

 is dark, a is the right au- 

 ricle, which receives the 

 dark venous blood from 

 all parts of the body. 

 From this it passes into #, the right ventricle, and this 

 forces it out toward the lungs, c. Here it becomes red or 

 arterial by exposure to the air which we breathe. It is 

 now returned to the left side of the heart, and is re- 

 ceived by the left auricle, which passes it into the left 

 ventricle. From thence it is sent to the general system, 

 /. Here it becomes dark by being used, and then re- 

 turns to the right auricle, , where we began to trace it. 

 30V. The diagram, Fig. 156, is the plan of the circula- 



tion in a Reptile. In 

 this, a is the right au- 

 ricle, which receives 

 the dark blood from 

 the general system,/", 

 and d the left auricle, 

 which receives the ar- 

 terial or red blood 

 from the lungs, c. But 

 the blood from the 

 two auricles mixes to- 

 gether in one ventri- 

 cle, 5, and this mixture of red and dark blood goes alike 

 to the lungs and to all the organs, as you see represented 

 in the diagram. The dark shading shows where there is 

 venous or dark blood, the light shading where there is 

 the mixture of venous and arterial blood, and the blood 

 is arterial or red where there is no shading. 



156 - 



