FOSSIL REPTILES. 167 



measure anticipated by the preceding portions of *' The Animal 

 Kingdom," and as we should exceed all reasonable limits by 

 dilating much on so extensive a subject. Occasional reference 

 to it, however, has been, and will be necessary, to enable the 

 reader to appreciate the distinctions between the present and 

 the past animal population of the earth. It will, indeed, be 

 necessary to treat a little more formally of specific characters 

 in reptiles, though our notices, of course, must be confined to 

 osteology : the other attributes of this class will be found in 

 their proper places in the present work. 



Every research on the differences of the productions of 

 nature must also infallibly conduct us to a consideration of 

 their relations. It is easy for the reader to perceive, that not- 

 withstanding the very varied proportions of the bones we have 

 hitherto surveyed ; notwithstanding the very singular external 

 forms which have often resulted from these varied proportions, 

 that, nevertheless, there exists among all the mammifera a sort 

 of common plan, a composition or combination, nearly similar ; 

 so much so, that every bone may be recognized by its uses and 

 position through every metamorphosis which it undergoes, 

 and in spite of all the augmentations and diminutions which it 

 experiences. Thus, in all the heads of this class, from man to 

 the balsense, we trace the frontal bones, the parietal, the nasal, 

 in a word, all the constituent parts of the cranium and face, 

 with such few and trifling exceptions as the absence of the 

 lachrymals in some species, and perhaps that of the interpa- 

 rietals in some others. The other apparent differences in the 

 number of the bones are referable, generally, to the greater or 

 less promptitude with which these bones unite, and the sutures 

 which distinguish them disappear. Thus the parietal in the 

 adult sometimes appears simple, sometimes double, and even 

 triple or quadruple, counting the interparietals, which always 

 finish by uniting together. But when we consider the animal 

 nearer to its birth, these anomalies disappear, and in the foetus, 

 or generally at the time when all the bones are still distinct, 



