11 INTRODUCTION. 



nation of the nature and affinities of extinct species, of whose organisa- 

 tion the teeth are not unfrequently the sole remains. 



Teeth consist of a cellular and tubular basis of animal matter 

 containing earthy particles, a fluid, and a vascular pulp. 



In general the earth is present in such quantity as to render the 

 tooth harder than bone, in which case the animal basis is gelatinous, 

 as in other hard parts where a great proportion of earth is combined 

 with animal matter. In a very few instances among the vertebrate 

 animals, the hardening material exists in a much smaller proportion, 

 and the animal basis is albuminous ; the teeth here agree in both 

 chemical and physical qualities with horn. 



True teeth consist of two or more tissues, characterized by 

 the proportions of their earthy and animal constituents, and by the 

 size, form and direction of the cavities in the animal basis which 

 contain the earth, the fluid or the vascular pulp. 



The tissue, which forms the chief part or body of the tooth, 

 has, hitherto, received no distinct and specific name in our 

 language ; a particular modification of it, which characterizes the 

 tusks of the elephant, is called ' ivory.' Some Anatomists 

 have extended the application of this term to the analogous sub- 

 stance in all teeth ; others have treated of it under the name of the 

 ' bone of the tooth'(l) or ' tooth-bone'; by the German Anatomists 

 it is termed ' knochensubstanz', ' zahnbein' and ' zahnsubstanz'; 

 and some of the latest and most close-thinking writers on 

 dental anatomy have preferred the literal translation of one or 

 other of these terms to the use of the word ' ivory', which 

 •unavoidably recalls the idea of the peculiar modification of the 



(1) Hunter, Natural History of the Human Teeth. Bell's Ed. 1835, Svo. p. 15, 16. 



