262 



THE DIGESTIVE SYSTEM 



The deposit of lime salts by the cylindrical cells of the inner 

 enamel layer, adamantoblasts, occurs earliest at the apex of the 

 dental germ. Thus, it is the enamel of the face of the tooth crown 



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FIG. 220. DEVELOPING TOOTH FROM A HUMAN FETUS 30 CM. LONG. 

 />, dentine; K, bone of the jaw ; RM, Malpighian layer of the oral nmcosa; S, en- 

 amel organ ; /SX 2 , enamel anlage of the permanent tooth ; VB, epithelial bridge still 

 uniting the anlages of the temporary and permanent teeth ; ZZ, disintegrating dental 

 ridge, x 30. (After C. Kose.) 



which is first formed, and this is therefore its thickest portion. 

 The enamel on the sides of the tooth crown appears later and 

 hence it gradually tapers in thickness as it approaches the neck 

 of the tooth, in which latter place the last formed enamel is 

 found. 



The nucleated bases of the cylindrical cells of the inner enamel 

 epithelium are also marked by a sharp cuticular margin and rest 

 upon the adjacent cells of the enamel pulp, the innermost cells of 

 which retain a characteristic epithelial appearance. The thin 

 layer formed by the uncalcified bases of the adamantoblasts, which 



