120 MICROSCOPIC ANATOMY OF THE TEETH 



at first in contact, become separated from one another by 

 a layer of stellate cells which fills the space between them. 

 This, ' the stellate reticulum ' eventually in Mammalia, 

 occupies the greater part of the area of the enamel organ 

 during the earlier stages of enamel development. 



The sides of the bell, the section of which appears as 

 a crescent, continue to grow downwards, the horns of this 

 crescent further enclosing the dentine papilla. 



The investment of the dentine papilla is considered not to 

 be produced by the upward growth of this papilla, but by 

 the down growth of the epithelial enamel organ around it. 

 Those cells which immediately invest the papilla between 

 the two horns of the crescent and form the inner layer of the 

 enamel organ become columnar in shape, and are known 

 as the ameloblasts or enamel-forming cells. 



The continuation of this layer on the outer side of the 

 stellate reticulum forms the external epithelium of the 

 enamel organ which separates it from the connective tissue 

 of the capsule. These cells, however, do not become 

 columnar in shape, as do those forming the internal epithe- 

 lium. A layer of rounded cells also appears, intervening 

 between the internal epithelium or layer of ameloblasts 

 and the stellate reticulum (fig. 68 (a)). This layer, called 

 the stratum intermedium, is only seen in contact with the 

 internal epithelium, and does not pass beyond the horns of 

 the crescent. 



The enamel organ is thus seen to be made up of four 

 distinct layers from without inwards : 



The external epithelium. 



The stellate reticulum. 



The stratum intermedium. 



The internal epithelium. 



The External Epithelium (figs. 69 to 72). This layer, which 

 forms the periphery of the enamel organ, is made up of 

 polygonal nucleated cells, which in later stages are often 

 elongated, their longer axes lying parallel to the surface. 

 The cells of this layer merge into those of the stellate 

 reticulum. 



It has been debated whether the cells of this layer have 

 any distinct function beyond that of limiting the boundary 



