THE DEVELOPMENT OF THE TEETH 



163 



aboral extension of the dental lamina, entirely free from the oral epithelium. 

 The anlages of the first permanent molars appear at seventeen weeks (180 mm.), 

 those of the second molars at six months after birth, while the anlages of the third 

 permanent molars or wisdom teeth are not found until the fifth year. The per- 

 manent dentition of thirty-two teeth is then complete. 



The internal cells of the enamel organs are at first compact, but later by the 



Oral epithelium 



Denial lamina 



Papilla 



Free edge of 

 the dental 

 lamina 



Aboral 

 prolonga- 

 tion of 

 dental 

 lamina 



Fig. 155.— A, B, C, D, diagrams showing the early development of three teeth. One of the teeth is 

 shown in vertical section (Lewis and Stohr). E, dental lamina and anlages of the milk teeth of the upper 

 jaw from a fetus of 105 mm. (Rose in Kollmann's Handatlas). 



development of an intercellular matrix the cells separate forming a reticulum 

 resembling mesenchyma and termed the enamel pulp (Fig. 156). The outer 

 enamel cells, at first cuboidal, flatten out and later form a fibrous layer. The 

 inner enamel cells bound the cup-shaped concavity of the enamel organ. Over 

 the crown of the tooth these cells, the ameloblasts, become slender and columnar 

 in form, producing the enamel layer of the tooth along their basal ends (Fig. 15S). 



