7 2 E VOL UTION AND DISEASE. 



been suggested by Mr. Eve, on very good grounds, that 

 the germs of teeth which have been suppressed in the 

 evolution of our species may make themselves ob- 

 noxious in an unexpected way. Teeth are formed in 

 part by down-growths of epithelium lining the floor 

 of the mouth ; these cellular down-growths, known as 

 enamel-organs, present distinctive features and are 

 easily recognized by practised histologists. The 



FIG. 34. A follicular cyst developed in connection with an 

 unerupted tooth of a Porcupine. The upper drawing 

 shows the effects of the cyst on the jaw. 



mouth of man is occasionally occupied by tumours to 

 which the name epithelial odontomes has been given ; 

 the peculiar feature of these tumours is that they are 

 composed of collections of cells in every way resembling 

 the enamel-organ. The opinion receives considerable 

 support from the fact that several carefully examined 

 specimens of this peculiar form of tumour have occurred 

 in cases where the number of teeth has been below the 



