DEVELOPMENT OF THE TEETH 



155 



(Figs. 159 B and 161). An enamel organ with dental papilla forms the 

 anlage of each tooth (Fig. 162). Ten such anlages of the decidual, or 

 milk teeth are present in the upper jaw and ten in the lower jaw of a 40 mm. 

 fetus (Fig. 165) . Their connection with the dental ridge is eventually lost. 

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

 by the development of an intercellular matrix, the cells separate, forming 



Oral epithelium 



Enamel organ 



A\ 



Dental groove 



I ^X / y*J^ 



I x^/ /^fe\ ' ^W ^/^W^^tf 



// // _^^ \; /^^-^ I/^T\ ^^^ 



IMM^ >>r \/ vb^5S^ " a 



Pa#*tt Enamel organs ^ cks f enamd or ans 



ABC D 

 FIG. 1 60. Diagrams showing the early development of three teeth, one in section (Lewis and 



Stohr). 

 Dental lamina 



Epidermis 



Outer enamel layer 

 Enamel pulp 

 Inner enamel layer 

 Dental papilla 



FIG. 161. Section through an upper incisor from a 65 mm. human fetus. X 7- 



a reticulum resembling mesenchyme, termed the enamel pulp (Fig. 161). 

 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 



