XVm INTRODUCTION^". 



THE EKAMEL. 



"The higher an animal is placed in the scale of or- 

 ganization, the more distinct and characteristic are not 

 only the various organs of the body, but the different 

 tissues which enter into their composition. This la^v 

 is well exemplified in the teeth, although in the com- 

 parison of these organs we are necessarily limited to 

 the range of a single primary group of animals. We 

 have seen, for example, that the dentine is scarcely 

 distinguishable from the tissue of the skeleton in the 

 majority of fishes; but that its peculiarly dense, un- 

 vascular, and resisting structure, which is the excep- 

 tionable condition in fishes, is its prevalent character 

 in the teeth of the higlier vertebrates. 



"So likewise with the enamel. This substance, 

 which under all its conditions bears a close analogy 

 with the dentine, is hardly distinguishable from that" 

 tissue in the teeth of many fishes. The fine calciger- 

 ous* tubes are present in both substances, and undergo 

 similar subdivisions, the directions only of the trunks 



siderable tliickness around the root, is of a yellowish-white 

 color ; but where, as on the crown of the tooth, it is exposed to 

 the chemical action of food and air, it presents a darker aspect, 

 and resembles an accumulation of tartar, for which indeed it 

 has becm mistaken. It fills up the infundibula of the grinders 

 and lines those of the incisors. It is pierced by all the vessels 

 which nourish the teeth." 



The editor of "The Veterinarian" (1849), in a "review" of 

 Mr. Mayhew's work, says: " Both English and French veteri- 

 nary writers have mistaken the crusta petrosa for tartar, not be- 

 ing" aware of its existence inside as well as outside of the tooth." 



* This word is peculiar to if not originated by Prof Owen. It 

 is synonymous with the word Ca'ciferous (limy). 



