THE ORAL EPITHELIUM. 39 



larges at its end, and, as seen in section, becomes 

 divaricated, so that it bears some resemblance to an 

 inverted letter Y ; or it might be better compared to a 

 bell-jar with a handle. This constitutes the early stage 

 of an enamel-germ, while beneath it, in the mucous 

 tissue, the dentine-germ assumes its papilliform shape. 

 The details of the process varying in different animals, 

 I will at once proceed to the description of the devel- 

 opment of teeth in the various groups." 



Prof. Tomes's views of the development of tooth- 

 germs in mammals are thus summarized by himself 

 ("Philosophical Transactions Koyal Society," 1875, 

 part i, p. 285) : 



"1. There is never, at any stage, an open groove 

 from the bottom of which papillee rise up. 



"2. That the first recognizable change in the region 

 of a forming tooth-germ is a dipping down of a process 

 of the oral epithelium, looking, in section transverse 

 to the jaw, like a deep simple tubular gland, which 

 descends into the submucous tissue, and ultimately 

 forms the enamel-organ. 



" 3. That subsequently to the descent of the so-called 

 enamel-germ, the changes in the subjacent tissue re- 

 sulting in the formation of the dentine papilla take 

 place opposite to its end, and not at its surface. 



"4 That the permanent tooth-germs first appear as 

 offshoots from the epithelial process concerned in the 

 formation of the deciduous tooth-germ (Kolliker), the 

 first permanent molar being derived from a primary 

 dipping down (like a deciduous tooth), the second de- 

 riving'its enamel-germ from the epithelial neck of the 

 first, and the third from that of the second (Legros 

 and Magitot)." 



