DENTINE 263 



will be more fully considered when treating of the * Sheath 

 of Hertwig '. 



In teeth in which enamel is present, however, the forma- 

 tion of an enamel organ always precedes the differentiation 

 of the cells of the papilla to form a dentine organ, although 

 calcification in Mammalia commences first at the summit of 

 the dentine papilla. In some fish the calcification of the 

 enamel precedes that of the dentine, and in marsupials, 

 although the process of calcification commences in the 



I 



FIG. 165. Enamel and osteodentine of Heterodontus (Cestracion). 

 Fuchsin stain by capillary attraction. ( x 50.) 



dentine, a very much larger proportion of enamel is soon 

 laid down above it ; this enamel, however, is not at this 

 stage fully calcified. 



When the dentine papilla is first seen to form a definite 

 dentine organ or tooth-pulp, and is enclosed above and at 

 the sides by the prolongation of the enamel organ, there is 

 no differentiation of the connective-tissue cells to form a 

 distinct peripheral layer beneath the enamel organ, but they 

 are uniformly distributed throughout the pulp. 



Very soon, however, larger rounded cells are seen accumu- 

 lating at the margins of the pulp. These cells have large 

 nuclei and a very small amount of cytoplasm, and many have 

 short truncated prolongations, but there is no appearance 



