FOSSIL REPTILES. 369 



The lateral prominence thus changes by little and little into 

 a true transverse apophysis. 



In the vertebrae which follow, this apophysis is tolerably 

 large, obliquely directed towards the top, and belongs entirely 

 to the annular part, so that when this part has fallen no trace 

 of apophysis remains in the body of the vertebra. 



The vertebrae of the tail are distinguished, as usual, by the 

 small facets which they have underneath, for the chevron 

 bones. 



These bones in the plesiosaurus, as in the crocodile, are 

 articulated under the juncture of the two vertebrae, so that 

 there are two facets for each of their branches, and each verte- 

 bra has itself four facets, two at its anterior edge, and two at 

 its posterior. 



These caudal vertebrae have also two transverse apophyses, 

 which, as in the young crocodiles, are attached by a suture ; 

 the impression of which remains visible on the body of the 

 vertebrae, below the suture which unites the annular part to it. 



The more we proceed in the examination of the tail, the 

 more we find these apophyses diminish in length and thick- 

 ness, and the marks left by their sutures diminish in pro- 

 portion . 



These forms of the vertebrae of the plesiosaurus, however 

 peculiar, and notwithstanding the length of their axes, incon- 

 testably resemble those of crocodiles, and especially of certain 

 fossil crocodiles, such as those of Caen, and the second found 

 at Honfleur, much more than those of the ichthyosauri, or 

 even of lizards. Mr. Conybeare was, therefore, perfectly 

 justified in considering the plesiosaurus as approaching the 

 crocodiles in many points, at the same time that, in its linea- 

 ments, it shows a relation to the ichthyosaurus. 



Without the surprising discovery of the skeleton which we 

 have mentioned, it would have been impossible to determine 

 the number of vertebrae which this animal possessed in each 

 of the portions of its spine. 



2 B 



