CHAPTER VI 

 THE TEETH OF REPTILES 



The second class of Vertebrates is the Reptilia, 

 which are more highly organized than the Fishes 

 and approach Mammals in some of the higher 

 forms. They are cold-blooded, breathe by means 

 of gills in the lowest types and by lungs in the 

 higher, and are covered with a tough, leathery 

 skin or by horny scales. 



The class is conveniently subdivided into two 

 main divisions, — (1st) the Batrachians (or Ama- 

 phibia), and (2nd) the true Reptiles. The Batra- 

 chians are the lowest form of Reptiles, and ap- 

 proach the Fishes in the degraded structure they 

 exhibit. They are the connecting link between 

 the fishes below and the true reptiles above them. 

 They breathe by means of gills, and are aquatic 

 during the first or larval stage of existence, and 

 later change to air breathers — as the common 

 Frogs, Toads, and Newts — on attaining maturity, 

 and live both on land and in water. Other forms 

 — as the Proteus — retain the gills through life. 

 The true Reptiles are lung-breathers, and live 



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