6 MICROSCOPIC ANATOMY OF THE TEETH 



Teeth are developed from the mucous membrane of the 

 mouth, and as stated by Beddard (2) : ' Developmentally 

 and histologically there are (in Mammalia) no fundamental 

 divergencies from the teeth of Vertebrates lower in the scale. 

 The teeth originate quite independently of the jaws with 

 which they are, later, so intimately connected, the inde- 

 pendence of origin being one of the facts upon which the 

 current theory of the nature of teeth is founded. The scales 

 of the Elasmobranch fishes consist of a cap of enamel upon 

 a base of dentine, the former being derived from the epi- 

 dermis and modelled upon a papilla of the dermis, whose 

 cells secrete the dentine. The fact that similar structures 

 arise within the mouth (i. e. the teeth) is explicable when it 

 is remembered that the mouth itself is a late invagination 

 from the outside of the body, and therefore the retention 

 by its tissues of the capacity to produce such structures is 

 not remarkable.' 



To the comparative anatomist and anthropologist, teeth 

 are of the greatest importance, as from their indestructible 

 nature they have survived the vicissitudes of time and 

 destructive agencies in the , most remarkable manner. 

 When found either alone or in association with remains 

 of a more perishable nature, they have indicated by 

 their form and structure the nature of the food and the 

 habits and affinities of long extinct forms, and have served 

 to forge the links of the evolutionary chain, from the 

 remotest appearance of vertebrate life on the earth to the 

 present time. 



The varieties of combinations of the different tissues, the 

 intricate patterns assumed in different teeth, and the 

 differences in the intimate structure of the dentine and 

 enamel, render the study of these organs throughout the 

 animal kingdom a source of unfailing interest and of the 

 greatest importance in all endeavours to obtain a better 

 comprehension of the evolutionary development of organized 

 beings. 



They render it still more evident that, so far as the 

 organic world is concerned, the doctrine of evolution as 

 stated by Darwin rests upon a sure foundation. The sur- 

 vival of the fittest is a demonstrable fact, and the principal, 



