DENTAL TISSUES. 



361 



237 



4iS^'Mi i' J^{ ^MKA' 





hardening salts of the enamel are not only present in far greater 

 proportion than in the other dental tissues ; but., in some animals, 

 are peculiarly distinguished by the presence of fluate of lime. 



Teeth vary in number, size, form, structure, modifications of 

 tissue, position, and mode of attach- 

 ment, in different animals. They 

 are principally adapted for seizing, 

 tearing, dividing, pounding, or grind- 

 ing the food ; in some they are 

 modified to serve as weapons of 

 offence and defence ; in others, as 

 aids in locomotion, means of anchor- 

 age, instruments for uprooting or 

 cutting down trees, or for transport 

 and working of building materials ; 

 they are characteristic of age and 

 sex ; and in man they have secondary relations subservient to 

 beauty and to speech. 



Teeth are always most intimately related to the food and habits 

 of the animal, and are therefore highly interesting to the physiol- 

 ogist. They form for the same reason most important guides to 

 the naturalist in the classification of animals ; and their value, as 

 zoological characters, is enhanced by the facility with which, from 

 their position, they can be examined in living or recent animals. 

 The durability cf their tissues renders them not less available to 



b 



a 



Section of tusk of Dugong, niagn. v. 



238 



^v 



^ 



**"& 





^^.^ -^-^" ^ -. Ss^u^3S2Sii% i ; 



: -* 



Magnified section of molar, Megatherium ; v vasodentine, f dentine, c cement, vi. 



the palaeontologist in the determination of the nature and affini- 

 ties of extinct species, of whose organisation they are often the 

 sole remains discoverable in the deposits of former periods of the 

 earth's history. 



The simplest modification of dentine is that in which capillary 

 tracts of the primitive vascular pulp remain uncalcified, and per- 



