DEVELOPMENT OF THE ENAMEL 



131 



a longitudinal direction (see Plate IV). The cells are generally 

 considered to be in close contact with one another, their 

 transverse section having an hexagonal form from mutual ap- 

 position, but Messrs. Underwood and Wellings (28 6) describe 

 intervals between them which they say appear to correspond 

 in diameter to the intercolumriar spaces in the formed enamel. 

 The proximal ends of the cells are square in shape before 

 the commencement of calcification and form a more or less 

 straight line where they are in contact with the tissue of the 





i^y^^fjif 

 ^^m^^^ 



a 



o 



P 



FIG. 77. Macropus. Before the commencement of calcification. The 

 cells of the stratum intermedium (s) are seen to be blended with those of the 

 internal epithelium (a), r. Stellate reticulum ; s. stratum intermedium ; 

 a. amelo blasts ; o. odontoblasts ; p. pulp. (x!50.) 



dentine pulp. When calcification has commenced each amelo- 

 blast is seen to be provided with a process which extends to 

 the surface of the forming enamel. This, the Tomes' process 

 of the ameloblast, is often seen very much pulled out and 

 elongated, especially in balsam mounted specimens, and 

 also has a tapered form in such preparations. 



In specimens, however, which have not been decalcified 

 or dehydrated, these processes are very little narrower than 

 the cell itself. They are very distinct in marsupials, and 

 their fine fibrillar structure is well shown, this being a 



K 2 



