LECTURES, 



LECTURE VII. 



W 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. n. B 



