CH. V.] 



DEVELOPMENT OF THE TEETH 



FIG. 69. 



Fin. 70. 



sac (fig. 71, s); and the rudiment of the jaw sends up processes 

 forming partitions between the teeth. In this way small chambers 

 are produced in which the dental sacs are contained, and thus 

 the sockets of the teeth are 

 formed. The papilla is com- 

 posed of nucleated cells ar- 

 ranged in a meshwork of 

 connective tissue, the outer or 

 peripheral part being covered 

 with a layer of columnar 

 nucleated cells called odonto- 

 blasts. 



These cells, either by 

 secretion, or as some think 

 by direct transformation of 

 the outer part of each, form 

 a layer of dentinal matrix 

 on the apex of the papilla, or 

 if the tooth has more than 

 one cusp, then at the apex 

 of each cusp. This layer is 

 first uncalcified (odontogen), 

 but globules of calcareous 

 matter soon appear in it. 

 These, becoming more numer- 

 ous, blend into the first cap 

 of dentine. In the mean- 

 while the odontoblasts have 

 formed a second layer of 

 odontogen within this (fig. 

 72), and this in turn becomes 

 calcified; thus layer after 

 layer is formed, each extend- 

 ing laterally further than its 

 predecessor ; the layers blend 

 except in some places; here 

 portions of odontogen remain, 



germ. FIG. 71. Ala'terstagej'c, outline ot epithelium 

 of gum; /, neck of enamel germ; /, enamel organ; 

 p, papilla ; s, dental sac forming ; / p, the enamel 

 germ of permanent tooth ; m, bone of jaw ; v, vessels 

 cut across. (Waldeyer and Kolliker.) 





down into the mucous membrane ; 2, palatine pro- 

 cess of jaw ; 3, Rete Malpighi. FIG. 70. Here the 

 section passes through one of the special enamel 

 germs which is becoming flask-shaped ; c, tf, epi- 

 thelium of mouth ; /, neck ; /, body of special enamel 



which in a tooth macerated 



for histological purposes get 



destroyed, and appear as the 



interglolular spaces (fig. 66), 



so called because bounded by the deposit of calcareous salts, which 



occurs, as we have already seen, in the form of globules. 



As the odontoblasts retire towards the centre, depositing layer 

 after layer of dentine, they leave behind them long filaments of their 



