CHAPTER VII 



EEPTILIA 



DEFINITION AND CHAEACTERS POSITION OF THE CLASS REPTILIA 



IN THE PHYLUM VERTEBRATA CLASSIFICATION SKULL AND 



VERTEBRAE. 



The recent Eeptiles comprise, broadly speaking, the Crocodiles, 

 Tortoises, Lizards, and Snakes. They are the only Vertebrates 

 which are cold-blooded, breathe by lungs, and have a median 

 occipital condyle. Another equally sufficient diagnosis is the 

 following : — Tetrapoda, with a median occipital condyle, with 

 nucleated red blood -corpuscles, and with complete right and 

 left functional aortic arches. A still shorter diagnosis is : — 

 Monocondylia with a scaly skin. 



If our diagnosis is to include the fossil Eeptiles we have not 

 only to discard the characters drawn from the soft parts as 

 unavailable, but we are forced to treat the condition of the 

 occipital condyle with caution, since there exist, or must have 

 existed, transitional stages between Eeptiles and Amphibia and 

 Mammals ; and the winged class Pterosauria does not permit us 

 to use the wings as a differential character for the Birds. In 

 fact, while the Eeptilia are sufficiently separated from the 

 Amphibia by their absolutely gastrocentrous vertebrae, it is 

 difficult to distinguish them as a class from the Birds ; hence the 

 term Sauropsida, which is intended to indicate the close relation- 

 ship of the Eeptiles to the Birds in opposition to the Mammalia, 

 and to the Ichthyopsida or Amphibia and Fishes. However, the 

 Eeptilia take up a very central position in the evolution of the 

 main classes of the Vertebrata. On the one hand, there is not 

 the slightest doubt that they are evolved from some branch of 



