40 MAMMALIA. 



,ly the actual jaw-bones fur- 



llislu-d \villi t> 



this a concentration of the tooth-material 

 accomplished, and connected with it we find 

 that concentration of force by which the mammal 

 more readily and surely overpowers its living prey, 

 and prepares it for use in the intestines, by mastica- 

 tion. In the dentition of the mammal we have not 

 regression but an advance in the organisation, 

 and a further diminution in two directions may be 

 ted. What has taken place with numerous 

 fishes has also happened in the case of some 

 of the Mammalia : under certain conditions of 

 nutrition teeth have become useless and have dis- 

 ared ; and, secondly, the fuller number of 

 i of the geologically older species has given 

 place to a dentition less numerous but more 

 d in form and action, and therefore more 

 ous. As an instance of the one direction, 

 ay take the jaw of a Ruminant, which shows 

 nt of the upper incisors; of the other direction 



\v of the Cat species. 



In order to understand the manifold forms of 

 must have some knowledge of the develop- 

 ment of the various substances that form the tooth, 

 the origin of the hard bright . immd (ebur), of the 



