CHAPTER XX 

 THE REPTILES 



The reptiles, although commonly associated in the 

 popular mind with the Amphibia, nevertheless constitute 

 a very distinct class which is really more closely related 

 to the birds than to any other group of vertebrate animals. 

 The reptiles are lung breathers at all periods of their life 

 and never have any gills, even in the young state. The 

 body is covered with scales or encased in a bony armor. 

 Living reptiles fall into the groups commonly designated 

 as Ophidia (snakes), Lacertilia (lizards), Crocodilia 



FIG. 140. A garter snake. (After Van Denburgh and Slevin.) 



(crocodiles and alligators), and Chelonia (turtles and 

 tortoises). 



i In the snakes the body has become greatly elongated 

 and very muscular. No limbs are present in most snakes, 

 but in the pythons and boas there are rudiments of hind 

 limbs and the pelvic girdle (see Fig. 235). Snakes are 

 regarded as in some respects degenerate animals which 

 have lost the limbs possessed by their ancestors. But 

 while they may have lost certain organs they have devel- 



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