MOUTH CAVITY. 163 



prceformativa, which lies between the odontoblasts and the inner 

 enamel cells. This membrane is converted into dentine and in 

 the beginning is a non-fibrillar structure. The development of 

 dentine starts at the apex of the tooth papilla. The odonto- 

 blasts send processes out into the fine canals which are formed 

 in the dentine, and these processes become the dental fibres. 



FIG. 119. 



Epithelium of 

 oral cavity 



Outer 



1 Neck f 

 <H enamel 

 ' P^Bj '["organ 



Kwmtef : I Dental 



,,/,rT ! ridgeof 



- perma- 

 if nent 



&'' / ! tootji 



Inner . '/''' 



enamel* e^ /^* Bone 



cell* ~*""trnbecH- 



\\, |B , : la' of 



loner 



jair 



Dental .-!&> ' ^ ; '' 



papilla 



An advanced stage in the development of a tooth in a three and a half months human 



embryo. X 65. 



Calcium salts are laid down in the fibrillar ground substance 

 in layers. Numerous small areas where calcification is incom- 

 plete or absent form the interglobular spaces. 



Soon after the beginning of the dentine formation the devel- 

 opment of the enamel starts. In the region of the future crown 



