76 W. H. F. ADDISON AND J. F. APPLETON, JR. 
surface epithelium surrounding the tip of the tooth, is a prepara- 
tion for the eruption of the tooth, and will serve as a resistant 
ring of tissue through which the tooth will be pushed at eruption. 
It may be looked upon as a protective device, to prevent adjacent 
tissues from being carried out by the erupting tooth. 
The typical enamel-organ seen on the labial side does not 
cover the apex, for the tall columnar cells give place here, first 
to cubical and then to flat squamous epithelial cells, which form 
but a part of the thick mass of stratified epithelium, constituting 
the epithelial sheath over the end of the dentine. The other 
layers of the functioning enamel-organ also lose their identity 
at the region where the ameloblasts cease to have their char- 
acteristic elongated form. As maintained by von Brunn (’87) 
and Sachse (’94), there is no enamel apparent over the dentine 
at the apex of the tooth. 
The cells representing the enamel-organ on the lingual side 
can be traced forward for a short distance as a two-layered 
stratum. These cells are flattened, with oval nuclei. Beyond 
this point only a single regular row of cells is apparent, and 
about half way along the length of the tooth-structure, even 
this ceases to be definite, and apparently here the mesenchymal 
cells of the peridental tissues have grown between and scattered 
these cells. As a result of this activity of the mesenchymal cells 
in this region, the enamel-organ now ceases to exist as a com- 
plete conical investment of the tooth. Approaching the apex 
of the tooth on the lingual side, one finds the prolongation of 
the epithelial sheath as a thin layer of flattened cells which 
thickens as it passes forwards into the epithelial sheath. 
The basal formative end of the enamel-organ consists of a 
thickened band of tissue, as shown in figure 18, and under higher 
magnification in figure 19. This end is thicker on the labial 
side than elsewhere and it curves inwards, as seen in longitudinal 
sections, thus considerably diminishing the diameter of the 
entrance to the pulp-chamber. The extremity of this mass of 
tissue (fig. 19, a), constitutes a common origin for the several 
layers of the enamel-organ and contains many dividing cells. 
A short distance (0.1 to 0.2 mm.) from the extremity (fig. 19, b) 
