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proportions as the former species. The annular 

 part of the vertebrae is also permanently distinct 

 from their body, articulating in a regular socket, 

 as in the ichthyosaurus ; and not anchylosing in the 



culated only to the end of the transverse processes ; at least, twenty- 

 eight appear to be thus circumstanced, whereas this takes place in 

 the three last of the crocodile only; in the other saurian animals, 

 however, all the ribs are thus borne. 



" Colonel Birch's specimen exhibits a series of sixty-three 

 vertebrae, but several appear to be missing, and it comprises only 

 the first twelve of the tail : there are as yet no means of surmising 

 even the number of caudal vertebrae. M. de la Beche has a conti- 

 nuous chain of eighteen middle dorsal ; and, in the late Mr. Calcott's 

 collection, there is another continuous series of nine, the eighth of 

 which carries the last short rib; this specimen seems fortunately to have 

 succeeded almost immediately to the former. The cervical and first 

 dorsal vertebrae appear to have possessed similar forms. They have 

 no transverse processes ; the line of suture with the annular part is 

 angular, and they have on either side of the body a double notch, 

 into which appears to have been inserted, by a double stem, a 

 tubercular process corresponding to the inferior tubercle in the 

 cervical and anterior dorsal vertebrae of crocodiles, and, like it, 

 bearing the false ribs which protected the neck and first true ribs. 



" The position of this double notch is near the bottom of the 

 side in the first vertebra, and gradually ascends till it almost 

 rises to and runs into the annular suture in the twelfth. In the 

 course of the succeeding four vertebrae, the upper of the two notches 

 runs into and extends the margin of the annular suture ; and, in 

 the next (the eighteenth), the lower notch becomes a distinct 

 tubercle ; thus two articulating surfaces are afforded, one on the 

 tubercle, and a second on the cavity formed by the prolongation 

 of the lip of the suture, of which the former must receive the head, 

 and the latter the tubercle of the anterior ribs. A similar structure 

 exists in the cervical and anterior dorsal vertebrae of the ichthyosau- 

 rus ; and it corresponds also in some degree, at least, in the office 

 of these parts, with the first dorsal vertebra of the crocodile, in 

 which the transverse process is not yet fully developed, and remains 

 only a tubercle. Atlengththe lower tubercle also disappears, and is 

 swallowed up in a still longer prolongation of the margin of the 



