202 MICROSCOPIC ANATOMY OF THE TEETH 



stages of its development and constitute the foundation 

 fibres of its matrix, are in many cases seen to arise from 

 cells, as will be described later. Before the commencement 

 of calcification there is no distinct differentiation of a peri- 

 pheral layer of cells so characteristic of the functionally 

 active pulp, but rounded cells are soon seen accumulating 

 at the periphery (figs. 114 and 115) with large nuclei and 

 a very small amount of cytoplasm, so that the cells appear 

 to consist almost wholly of nuclei. 



FIG. 116. Macropus. Rounded cells forming a definite layer at the 

 margin, p. Pulp ; o. first indication of odontoblast layer ; a. ameloblasts ; 

 s. stratum intermedium ; r. stellate reticulum. ( x 150.) 



In fig. 116 short processes can be detected prolonged from 

 the cytoplasm of the cells, but no definite dentinal fibril has 

 appeared. In a later stage, shown in fig. 117, the outer cells 

 form a definite layer, and their prolongations extend as 

 the dentinal fibril traversing the first deposited colloidal 

 substance in which calcification later takes place. It is 

 seen in this illustration that the dentinal fibril is a broad 

 expansion of the cell substance and not the narrow process 

 often shown in shrunken preparations. 



The early stages of development of the cells of the human 



