278 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



as the four large anterior caudal vertebrae in the Mantellian Collection, 

 also assigned by the author of the Report to the Cetiosaurus brevis, 

 cannot be transmuted into the vertebrae in question by any changes 

 occurring in a consecutive series, there is left for that animal only some 

 terminal caudal vertebrae ; while to complete the tail of the Iguanodon 

 just those are wanting ; 4thly, but independently of the evidence 

 furnished by the Maidstone specimen, we have seen examples which 

 point out the series of changes by which these angular vertebrae are 

 produced from those of the middle caudal region. These changes, 

 again, are not greater than those that take place in the tail of the 

 Hylaeosaurus, and other extinct reptiles, as well as in that of many 

 mammalia. 



" Let us look for a moment at the vertebrae of the tail of the Mosa- 

 saurus as contrasted with those of other regions of the spinal column in 

 that reptile, and we shall then be prepared to admit far greater modifi- 

 cations than are here assumed. Could we a priori correctly restore the 

 vertebral column of any animal from scattered fragments, belonging to 

 different individuals, without making any allowance for the changes 

 occurring in the series of segments composing that column ? 



" In the form of the terminal caudal vertebrae we may expect to find 

 a very great similarity even in remote genera, and hence it is unsafe to 

 base a generic character on their peculiarities. The genus Cetiosaurus 

 (restricted to the species medius and longus from the Oolite) is founded 

 chiefly on such trivial distinctions, and we may refer to it any caudal 

 vertebra of considerable dimensions with plano-concave or biconcave 

 facets, not referable to other known and perfectly determinate genera, 



a reference to the " Geol. Trans." vol. ii. New Series, PI. XV. figs. 1, 3. 

 The figures were drawn by Mr. Scharf, and I can vouch for their accuracy ; 

 but without the actual connexion of vertebrae with such character, with 

 known parts of the skeleton, I should not consider this opinion deci- 

 sive. H. von Meyer has justly remarked, "that conclusions drawn 

 from a single part of a fossil skeleton, and applied to the whole, must 

 necessarily prove 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 saurian, 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 different 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 appa- 

 ratus of the teeth of the fos&il saurians, which we have to consider, there 

 is usually expressed a combination of the characters of the crocodile 

 with those of the lacertse ; 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." "Palceo-^ 

 logica. Geschichte der Erde und ihrer Geschopfe ; Hermann von Meyer." 

 Frankfort, 1832. 



