284 Structure of the Fossil Saurians. 



afterwards becomes a reptile. The observations which I have 

 introduced above respecting the analogies existing between 

 fishes and birds, and particularly between the Mammalia on 

 the one hand, and reptiles on the other, is equally dis- 

 tinctive for reptiles. Among the Ophidians there are legiti- 

 mate snakes, in which rudiments of hind limbs are to be 

 observed *, even exteriorly, by which these animals are con- 

 nected with creatures possessing limbs. 



The fossil Saurians, from the transition beds, are to be com- 

 pared, with reference to their organs of motion, to the Mam- 

 malia with heavy limbs, to the Mammalia with limbs adapted 

 for swimming, and to the flying Saurians. Single parts of 

 the skeleton of the flying Saurian (Pterodactyle), remind us 

 of the Qrnithorhynchus. If, however, in these fossil Saurians 

 the structure of one part of the body approaches that of the 

 Crocodile; in the same individual, the structure of another part 

 reminds us rather of that of the Lacertoe. Hence it follows, 

 that conclusions drawn from a single part of the skeleton, 

 and applied to the whole, have necessarily proved erroneous, 

 and have deceived even such anatomists as Camper. While we 

 remain ignorant of the plan according to which the structure 

 of the whole animal is formed, but little can be deduced from 

 the single parts. A fossil Saurus, with an elongated beak, 

 like that of a Gavial, is not necessarily from that circumstance 

 alone a Gavial, a creature for which it has commonly been 

 taken : the other portions of the skeleton may be totally dif- 

 ferent from this latter animal. How little we can infer from 

 one fossil Saurian as to the structure of another, is shown 

 by the Megalosaurus and Geosaurus, the teeth of which are 

 very similar, while they have nothing else in common. In 

 the apparatus of the teeth of the fossil Saurians, which we 

 have to consider, there is usually expressed a combination of 

 the characters of the Crocodile with those of the Lacertae ; to 

 which are occasionally added peculiarities which remind us 

 of the apparatus of the teeth of Fish, of Cetacea, and even 

 of the land Mammalia, both herbivorous and carnivorous. 

 The vertebral column, in almost all these animals, is pro- 

 vided with a surface which is concave behind, instead of 

 convex, like that of the living Saurians, and may hence 

 be compared with that of the Cetacea, Fish, or Batrachians, 

 without its having been known that the fossil Saurians, in 

 their youth, might have possessed a nature similar to that of 

 fish, and have breathed, in some measure, by means of gills. 

 The observation, therefore, which Mantellf applied to some 



* Mayer Nov. Acta Acad. Leop. Carol. Nat. Cur., 12. 

 f Geol. Sussex, C5. 



