GREAT USE OF THE CEMEHT. 45 



to bony matter. A hard and beautiful crystallization 

 is formed on the membrane without, and so we have 

 the cutting tooth covered by its enamel. 



" In the formation of the grinders there are origin- 

 ally five membranous bags in the upper jaw and four 

 in the lower. The jelly in thc-m 

 gives place to bony matter, 

 which is supplied by little ves- 

 sels, and which is represented 

 by the darker portions of the 

 cut with central black spots. 

 Tlie crystalhzation of enamel 

 may be traced around each of the bags, and there 

 would be five distinct bones or teeth but for the fact 

 tliat a third substance is now secreted. (It is repre- 

 sented by the white spaces). It is a powerful cement, 

 and through its agency the bones are united into one 

 body, thus making one tooth of tiie five. This being 

 done, another coat of enamel spreads over the sides, 

 but not the top, and the tooth is completed." 



Dr. Robley Dunglison's theory of the development 

 of the human teeth is in principle the same as Prof. 

 Youatt's theory regarding those of the horse. In his 

 "Medical Dictionary," article "teeth," he says: 



"The incisor and canine teeth are developed by a 

 single pomt of ossification, the lesser molars by two, 

 and the larger by four or five." 



Surgeons M. H. Bouley and P. B. Ferguson believe 

 that the teeth are the combined product of the secre- 

 tion of the |)ulp and of the membrane vvdiich lines the 

 alveolar cavities. They say that the question as to 

 whether the sensibility of the teeth is inherent in the 

 dental substance itself, or resides exclusively in the 



