484, J. T. WILSON AND J. P. HILU. 
corresponding tooth in the upper jaw that little special descrip- 
tion need be given. It is indeed just a little in advance of its 
opponent. In particular we find that in the hinder part of 
its enamel-organ an important differentiation has set in, of 
which no trace is as yet visible in the upper tooth. Fig. 40 
shows that the cup-like cavity of the enamel-organ is now in 
process of subdivision into two, and that, corresponding to this 
the dermal papilla exhibits two very slight pointed projections. 
Here plainly we have the earliest stage in the production of 
more than one cusp in the case of an enamel-organ which, at 
the previous stage of its development, was a perfectly simple 
cup, with a correspondingly simple papilla. The figure repre- 
sents, in fact, an appearance which has been already claimed 
by Rose as illustrating the earliest and most primitive con- 
dition of a multicuspidate tooth. In the case of the deciduous 
premolar in Perameles, it can be proved that such is not the 
case; and that here, at least, cusp-formation is a secondary 
complication, introduced at a period subsequent to the forma- 
tion of the primitive dermal papilla. 
As in the upper jaw, the dental lamina behind dpz is the 
prolongation of the residual lamina in the region of the latter, 
and some distance behind it is continued into the Anlage of 
the first molar. There is not the same sudden elongation here 
as in the upper jaw, and it can therefore be plainly seen that 
the inner lip of the most anterior part of the cupped enamel- 
organ of mz is the direct continuation of the dental lamina, 
the rest of the enamel-organ having plainly arisen by out- 
growth from the labial surface of the lamina, as we have seen 
to be the case in other tooth rudiments. On the other hand, 
the residual dental lamina has not liberated itself from the first 
molar Anlage in the lower jaw as in the upper, except in so far 
that the enamel-organ gradually diminishes posteriorly, and 
finally disappears as a mere labial excrescence of a thickened 
lamina. The latter is continued backwards, and very shortly 
behind it develops another laminal excrescence, which when 
followed is seen to form the labial boundary of the cup of the 
papillated enamel-organ of mz (fig. 41). This tooth now ex- 
