THE TEETH OF VERTEBRATES 49 



jaw so as to enable the animal to use the tooth 

 (Fig. 12). 



The thecodont tooth is ankylosed in a socket 

 and is the type found in the higher reptiles and a 

 few fishes. The tooth is more firmly supported in 

 this form than in any other (Fig. 13). 



4th. By Implantation in a bony socket, as 



Fig. 12. — Mandible of Eel (Anguilla rostrata) , showing pleurodont 

 attachment of teeth. 



found in some Eeptiles and in the entire class of 

 Mammalia. It is the method of attachment in 

 man. There is an intervening membrane, a modi- 

 fied periosteum, between the root of the tooth and 

 its alveolus, and a special bone of attachment, 

 called the alveolar process, which is raised up 

 around the root to support the tooth as it comes 

 into place, and is absorbed when it is lost (Fig. 

 14). 



