Structure of the Fossil Sauriasis. 283 



certae.* The number of fossil Saurians is still comparatively 

 small ; which may probably arise from the circumstance of 

 their requiring to be wrought out from the solid rock. The 

 examples of these animals which, in earlier times, ruled over 

 the earth, are however sufficient to enable us to increase the 

 extent of the Saurian world, and to arrange it in a systematic 

 manner. 



The difference of the Crocodiles and the Lacertae depends 

 chiefly on the strongly scaled skin of the former, and the 

 lightly scaled skin of the latter ; on the system of the teeth, 

 their formation, number, &c. Among the fossil Saurians, 

 these characters are by no means invariably preserved. The 

 general form of the head, the structure of the teeth, the situ- 

 ation of the teeth in the alveoli (either separated, or placed in 

 a common channel), the strongly or lightly scaled skin, the 

 situation of the apparatus of hearing, or of the nasal canal, 

 as well as other portions of the structure, do not afford cha- 

 racters which enable us to class the animals with a sufficient 

 degree of precision or facility. I am therefore induced to 

 avail myself of the developement of the organs of motion as 

 the foundation of the chief types among the Saurians, and to 

 attempt their systematic arrangement by these characters. The 

 structure of the organs of motion has not a mere exterior im- 

 portance : for these organs open to the creature the medium 

 in which it moves, feeds, and chiefly exists, and to which the 

 other parts of the structure must be adapted. The further 

 division can be determined by other single parts of the struc- 

 ture. The paucity of types of the Saurians, at the present 

 moment, proceeds from the circumstance of their being sub- 

 arranged under the division A. of the following scheme. The 

 fossil species enable us to arrange the Saurians in a far more 

 perfect manner than the other reptiles; the Mammalia, also, are 

 completed by their fossil species. These last receive, however, 

 at the utmost, only an accession of genera; while, among the 

 the existing arrangement of Saurians, whole families have to be 

 inserted. The Saurians, by this means, receive an extension 

 and a systematic classification, by which they are established 

 as Flyers, Swimmers, and Walkers [Flieger, Schwimmer, und 

 Ganger], since they unite in themselves types of different classes 

 of animals. A classification of animals, accordinn; to form is 

 strikingly to be observed among the Batrachians, which un- 

 dergo an actual metamorphosis. The same individual breathes 

 first, while young, by means of gills, is actually a fish and 



* The Hyleosaurus of Dr. Mantell has the coracoid of the Lizard, with 

 the omoplate of the Crocodile. Vide Geology, S. E. of England, — Ed. 



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