DEVELOPMENT OF THE ENAMEL 149 



characteristic form, and large highly refractive globular- 

 bodies are seen in their place (fig. 83). 



Leon Williams, in summing up this part of his subject, 

 says : ' It is now perfectly evident, however, that in the 

 development of enamel the cells of the stratum intermedium 

 play the most important part in the selection from the blood 

 of the material for the construction of this tissue. The 

 formation of enamel begins, however, before the full develop- 



FIG. 83. Developing tooth of Macropus. Late stage of calcification 

 of the enamel, e. Enamel ; a. ameloblasts ; g. globular bodies in stratum 

 intermedium. No Tomes' processes are visible. ( x 700. ) 



ment of the stratum intermedium, and it is highly probable, 

 as has been pointed out by previous writers, that the material 

 for the commencement of enamel formation is stored in the 

 stellate reticulum.' 



The cells of the internal epithelium of the enamel organ, or Amelt/ 

 ameloblasts, are in Mammalia the active agents in the forma- l 

 tion of the enamel. These are elongated columnar cells with 

 large nuclei, which are situated in that part of the cell most 

 distant from the forming enamel (figs. 84 and 85 and Plate IV) . 



The cell shows a fine reticular structure, and in thin 

 sections the fibrillar constituents are seen to be arranged 

 more or less parallel with the long axis of the cell. The 



