REPTILES. 189 
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, @ is the right au- 
ricle, which receives the 
dark venous blood from 
all parts of the body. 
From this it passes into 6, the right ventricle, and this 
forces it out toward the lungs, ¢. Here it becomes red or 
arterial by exposure to tlfe air which we breathe. It is 
now returned to the /efé 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, 
J. Here it becomes dark by being used, and then re- 
turns to the right auricle, a, where we began to trace it. 
307. The diagram, Fig. 156, is the plan of the circula- 
- tion in a Reptile. In 
this, @ is the right au- 
ricle, which receives 
the dark blood from 
the general system, 7, 
and @ the left auricle, 
which receives the ar- 
terial or red blood 
from the lungs, ¢. But 
the blood from the 
two auricles mixes to- 
Reese: gether in one ventri- 
cle, 6, 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. 
