Back view of skull of Crocodile. 

 0, single occipital condyle ; q, quadrate bone. 



to Fossil Reptiles and Fishes, p. 1), Dinosaurians (huge terrestrial 

 Reptiles far exceeding in size our largest Crocodiles, p. 8), 

 Ichthyosaurians, and IMesiosaurians (large marine creatures, 

 Geological Guide, pp. 32, 47), Dicynodonts (p. 55), Crocodiles, 

 Lizards, and Turtles lived in abundance; Snakes, however, did not 

 appear before the Tertiary period. At present some 4000 species 

 of Reptiles are known, which are unequally divided among five 

 Orders, viz. Crocodilia (Crocodiles and A]\igaiors),Rhynchocejj/ialia, 

 Lacertilia (Lizards), Ophidia (Snakes), and Chelonia (Tortoises 

 and Turtles). 



In this classification of Reptiles the naturalist is guided much 

 more by the structure of the skeleton and the other internal organs 

 than by the external appearance. In fact, in Reptiles, as in many 

 other classes of the Animal Kingdom, outward similarity is decep- 

 tive as to the natural relationship — that is, as to the degree in 

 which they are related to each other as descendants from a more or 

 less remote common ancestor. Take, for instance, a Crocodile, a 

 Lizard, a Slowworm, and a Snake. The observer who, like the 

 naturalists of the last and preceding centuries, is guided by external 

 appearance only, would without hesitation place the Crocodile and 



