TEETH. 7 I 



pulp they come in contact with the outer cells. The two layers form the 

 epithelial sheath of the root (Fig. 86). 



The adamantoblasts are columnar cells with elongated nuclei toward 

 their outer ends. (Since the enamel organ is an inpocketing of ectodermal 

 epithelium, it is clear that the basal surfaces of the enamel cells are toward 

 the mesenchyma, and the outer surfaces toward the enamel pulp.) 

 Diplosomes have been found near the nuclei. There are terminal bars 



Cuticular border. Enamel prisms. Cement substance. 



Calcified,, .uncalcified dentine. 



Enamel pulp. Rectangle enclosing the portion 



Odontoblasts. Pulp, of the tooth shown highly magni- 



Outer enamel cells. Inner enamel cells fied in the adjoining part of the 



(adamantoblasts). figure. 



FIG. 79. PORTION OF A LONGITUDINAL SECTION OF AN INCISOR TOOTH OF 



A NEWBORN KITTEN. X 300. 



In this section the young enamel prisms have been pulled out of their spaces in the cement substance. 

 (The cement of the enamel must not be confused with the cement which covers the root.) 



and a cuticular border at the basal surface, toward which the protoplasm 

 contains granules which blacken with osmic acid. Between the cells 

 there is a cement substance. The long columns (prisms) which grow out 

 from the basal surface of the cells are likewise surrounded by cement 

 substance. The columns at first are not calcified [and are often called 

 Tomes' processes]; they have a honey-comb structure and tend to split 

 into longitudinal fibers. They may connect with one another by wing- 

 like expansions. Later both the prisms and the cement substance become 

 calcified, the former increasing in diameter at the expense of the cement. 

 Eventually little (2-5%) or no organic matter remains in the enamel. 



The prisms extend across the enamel from its inner to its outer surface. 



