LECTURES, 
^x, ^c. 
LECTURE VIL 
E are now arrived at a class or tribe of the 
animal kingdom highly remarkable both for sin- 
gular external appearance and internal conforma- 
tion. These animals differ from viviparous qua- 
drupeds and from birds in the structure of those 
important organs the heart and lungs. The 
heart in these amphibious animals may be said to 
have but one ventricle or cavity, instead of two as 
in viviparous quadrupeds and birds. For though 
some variation takes place in the formation of 
this organ in the different tribes of the Amphibia, 
yet the general effect with respect to the circula- 
LECT. II. 
B 
