iilrO STRUCTURE AND ADAPTATION OF TEETH 



temporary inhabitants,; but the science of histology 

 (or the knowledge of tissues) proceeds still farther, 

 and the accomplished comparative anatomists of 

 our own country are now enabled, by applying the 

 microscope to the examination of the minute frag- 

 ment of a tooth, to identify the family and even the 

 genus of an animal. 



If we examine a polished section of human den- 

 tine by the unassisted eye, it presents a satin-like, 

 opalescent appearance, arising from the presence 

 of innumerable fine tubes penetrating the entire 

 structure, — an organization so clearly elucidated by 

 Mr. Tomes, in his " Dental Physiology," that I 

 need only refer you to the earlier chapters of that 

 invaluable work. The microscope shows that there 

 are distinguishing characteristics in the forms and 

 arrangements of these tubes, in each of the various 

 tribes : supplying a key whereby their true place 

 in the scale of creation may be recognised. 



ARRANGEMENT OF DENTINAL TUBULI. 



Fig. ^1 .—Human. 



