FROG. 
29 
covers the lower jaw will be perceived, and every 
time this part moves, a corresponding twirling mo- 
tion may be observed in the nostrils. By this twirl 
the air is let into the mouth, and the skin be- 
comes dilated; whence it passes through a slit for 
that purpose behind the tongue into the lungs, 
from whence it is again expelled by the mus- 
cles of the abdomen, and followed by the same 
expansion of the cheeks and twirl of the nostrils. 
Thus the lungs are filled by the action of the mus- 
cles of the jaws, and frogs swallow air nearly in the 
same manner as we swallow' food. 
