DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 459 
what enlarged, and forms a swelling whose outer aspect 1s 
somewhat flattened, while its fundus is more rounded and is 
somewhat mesially inflected. The outer, more flattened por- 
tion now comes to project labially, and is seen to consist 
mainly of cells, the chromatin of whose nuclei is evidently in 
the active phase. This feature causes this portion of the mass 
to appear pretty definitely differentiated with a haematoxylin 
stain. Some sections further back the labial projection of the 
lamina is deeply indented by a dermal papilla (fig. 12), so as 
to form a labially directed enamel-organ (d7;) in the cup- 
shaped stage. This is as yet incompletely differentiated from 
the common mass of the swollen dental lamina. The entire 
enlargement of the lamina in this situation corresponds to the 
region of the first incisor, and the labially cupped enamel- 
organ, in process of differentiation, is the Anlage of the first 
milk incisor (diz). This rudimentary tooth is shown in 
subsequent stages to undergo a precocious though imperfect 
development into a minute calcified tooth. 
Opposite the papilla of di; the main mass of the dental 
lamina has become considerably enlarged, and the increase in 
bulk continues behind the rudiment of the milk-tooth. Part 
of this posterior thickening doubtless represents the hinder part 
of 7, but the more posterior portion must provide the material 
for the development of tz. This is rendered certain by com- 
parison with the succeeding stage (111), for in both stages the 
dental lamina makes an abrupt turn outwards and runs trans- 
versely for a very short distance, instead of antero-posteriorly. 
Now in Stage 11 it becomes certain that 7, is developed at 
the postero-external limit of this transversal part of the lamina, 
and 7; at its antero-internal extremity. Further, in the 
present stage the short transversely running part of the 
lamina commences immediately posterior to the thick part of 
the lamina which lies behind di; ; whilst at the outer end of the 
same short transverse part of the lamina appears a new 
thickening. This, as we shall see, is the only other swelling 
in front of the canine, and it corresponds exactly in position 
to ig in Stage 111. 
