282 Structure of the Fossil Saurians. 



A'ngues. The arrangement of the apparatus of hearing 

 induced Blainville to place the Crocodiles in a peculiar 

 division, which he terms Emydosaurian, in order to express 

 their place between the Lacertae and the Tortoises. Geoffroy, 

 however, does not agree in this arrangement, he considers the 

 pterygoid (a bone of the head, which in the human subject is 

 the inner palatal bone), to be distinctive as regards the Cro- 

 codile, and relying on this part of the structure, distinguishes 

 the Caiman, Crocodile, and Gavial ; as he also further divides 

 these from the Lacertae. The arrangement of the nasal 

 canal appears to him to afford a satisfactory mark of distinc- 

 tion ; since the elongation of it varies in a very remarkable 

 degree in different animals. In the Mammalia this canal is 

 more important than in reptiles ; in crocodiles it is still more 

 so, for the opening lies behind the strongly developed ptery- 

 goid. The study of the ear also enabled him to distinguish 

 several genera among the crocodiles which had hitherto been 

 united under the name of Caimans. 



The structure of fossil animals of the Crocodile and Lizard 

 species has induced me to select Brongniart's nomenclature 

 of the Saurians, and to include in it animals which are com- 

 monly termed Crocodiles, Monitors, or Lacertae. The differ- 

 ence of species is usually determined by the structure and 

 colour of the skin. Differences in the form of the single 

 parts of the osteology afford, according to their importance, 

 occasion for the establishing a genus or subgenus ; while some 

 numerical relations connected with them establish a family or 

 a distinction of still greater extent. Among many of the fossil 

 Saurians, however, a distinction of species is almost impossible, 

 since the parrs which would distinguish them have become 

 obliterated by their long continuance in the earth. Usually 

 only those portions of the bones are discovered, the dif- 

 ferences of which serve to indicate either subgenera or 

 genera ; but in some of the earlier fossil Saurians, the 

 very diversity of species appears to be clearly impressed on 

 the skeleton. Among the Saurians, however, from the so 

 termed transition formations, differences have been considered 

 as merely specific, which are, in fact, of more importance. 

 Cuvier arranges these fossil Saurians into the Crocodiles, the 

 Monitors, and the Lacertae, or the Saurians in the stricter 

 sense. They are, however, for the most part formed ac- 

 cording to a plan which differs from the living Saurians, 

 in its far greater abundance of types (an abundance, which 

 our knowledge of the existing animals would not lead 

 us to expect) ; and also by its blending those structures 

 which are separated in the legitimate crocodiles and La- 



