THE SKIN. 



205 



The Teeth. The development of the teeth presents close anal- 

 ogies to that of the hairs. They also first appear as little masses 

 of cells, growing into the connective tissues of the alveolar proc- 

 esses from the stratified epithelium covering them. Into the bases 

 of these masses connective-tissue papillae are developed, which 

 eventually become differentiated into the pulp of the tooth-cavities. 

 The epithelial cells which immediately surround these papillae be- 

 come elongated to a columnar form and then become converted 



FIG. 183. 



Y 



Section of developing tooth. From embryo of rabbit. (Freuiid.) ep, epithelium of gum; 

 a/i, epithelial cells forming outer layer of the enamel-pulp of the temporary tooth ; L, sim- 

 ilar layer belonging to the rudiment of the permanent tooth ; &r, enamel-pulp ; p, dental 

 pulp of the tooth-cavity ; d, dentin; v, bloodvessels; B, rudiment of second or permanent 

 tooth ; a, embryonic connective tissue of the alveolar process. 



into or elaborate the tissue of the enamel. The superficial cells 

 of the papillae likewise elongate and produce the dentin. The 

 cement which constitutes the outer layer of the root of the tooth 

 is bone, and is developed from the foetal connective tissue in that 

 region (Figs. 182 and 183). 



Only a brief description of the structures entering into the forma- 

 tion of the fully developed tooth can be given here. For a more 

 detailed account of them the student is referred to special works on 

 the subject. 



