133 



NORMAL HISTOLOGY. 



to those of bone-lamellre. The dentine-matrix, deposited through the ac- 

 tivity of the odontoblasts, is for a time uncalcined. The deposits of lime- 

 salts occurs first over the apex of the papilla and next the enamel, a zone of 

 uncalcified matrix around the pulp- cavity marking the youngest dentine. 

 The calcareous material is deposited in the form of minute spheres, the den- 

 tine-globules, calcification being 

 completed by the subsequent fill- .. *. ' 

 ing of the interglobular clefts. 

 When for any reason calcification 

 is incomplete, these clefts remain 7^,pentaiiedge 



Thickened 

 oral- 

 epithelium 



Labio-dental 

 strand ~ 



' 



Mesoderm . i '. ' ' T ;"-{" " 



''';'*' Enamel- 

 organ 



Outer layer 



Middle ; 



layer 

 Inner layer 



of enamel 



organ 



Dental 

 papilla" 



l"^,Y ; '::'' : ' 



, 



'. 



Outer 

 - layer of 



eriamel- 

 organ 



j Dental 



T papilla 



Epithelial 



sheath 



FIG. 177. Sections showing four early stages of tooth-development. A, B, X 75; C, D, X 50. 



uninvaded and are recognized as the interglobular spaces. The dentine- 

 matrix differs from that of bone in being produced by a single set of cells, 

 while the bone-matrix is the collective work of relays of osteoblasts which, 

 while contributing their increment, become imprisoned in the lacunae within 

 the matrix that they have formed. In human dentine, on the contrary, the 

 odontoblasts remain on the surface and only exceptionally become enclosed 

 within the dentine-matrix. With the completion of dentine-production, the 

 odontoblasts become narrower and smaller and later exhibit evidences of 



