44 TOOTH-GERMS. 



from this germ and passing backward, to serve, at a 

 later period, in forming the permanent tooth." 



In another part of his work Prof. Chauveau says: 



" The follicle in which the incisor teeth are devel- 

 oped shows only two papillae. One, for the secretion 

 of the dentine, is lodged in the internal cavity of the 

 tooth, and is hollowed into a cup-shape at its free ex- 

 tremity; the other is contained in the external cul-de- 



In describing the simplicity of the structure of the 

 horse's canine teeth (tushes), Prof. Lecoq says: 



"The disposition of the developing follicle is in har- 

 mony with the simplicity of their structure. At the 

 bottom there is a simple and conical papilla for the 

 internal cavity; on the inner wall, a double longitu- 

 dinal ridge, on which are molded the ridge and grooves 

 on the inner face of the tooth." 



Prof. William Youatt's theory of the development 

 of horses' teeth is unique. He is probably correct 

 about the bones or processes being separate, and his 

 claim that they are solidified by the cement is certainly 

 philosophical ; but he differs from all other authorities 

 about the enamel completing the formation of the 

 tooth, for it is a well-known fact that a virgin tooth 

 is enveloped by cement (its protecting varnish), which 

 wears off as soon as the tooth is brought into use. He 

 says ("The Horse," p. 223) : 



"A delicate membranous bag, containing a jelly-like 

 substance, is found in a little cell within the jawbone 

 of the unborn animal. It assumes by degrees the 

 shape of the tooth, and then the jelly begins to change 



