STRUCTURE AND GROWTH OF INCISOR TEETH fal 
although the outer layer still persists as a layer of flattened cells. 
Thus lingually the enamel-organ is represented by only two 
rows of cells—one representing the inner, the other the outer 
layer of the enamel-organ. . 
Fig. 15 Cross-section of developing lower incisor of 1-day albino rat, show- 
ing the great development of the ameloblasts on the labial side, and the thin- 
ness of the enamel-organ elsewhere. The space between the ameloblasts and 
the dentine is an artefect, and was formerly partly filled by the enamel, which 
has disappeared in the process of decalcification. In the layer of odontoblasts 
are seen the nuclei of the endothelial cells of the walls of capillaries. 110. 
Two days old 
Figure 16 shows a longitudinal section of a 2-day upper incisor. 
The epithelial enamel-organ is continuous over the whole tooth, 
but only shows its specialized functioning structure on the labial 
side. On the lingual side it is still intact and consists only of 
two rows of cuboidal or flattened epithelial cells. On the labial 
side, along the region where enamel has been formed (fig. 17) the 
