DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 477 
other premolar germs. On the contrary, it is com- 
paratively far advanced in structural differentiation 
by the time there appears any trace at all of the 
anterior premolars, or more than very slight traces 
of the formation of the enamel-organs of any perma- 
nent tooth whatever. 
The vertical elongation of the cross-section of the dental 
lamina just anterior to dp? has been referred to. Just in 
front of the plane at which the enamel-organ of the latter 
tooth comes into view the dental lamina is higher than at 
any more anterior part of the premolar region, and as high as 
it is at the canine thickening. This height is retained by the 
residual lamina opposite to dp®. Towards the hinder part of 
the tooth the lamina becomes separated off from the oral epi- 
thelium. 
A couple of sections or so behind the disappearance of the 
last trace of the enamel-organ of dp3, the free margin of the 
dental lamina undergoes an abrupt further elongation, i.e. it 
suddenly penetrates considerably deeper into the connective 
tissue to be prolonged into the rudiment of m+, which forms 
immediately behind as a large cup-shaped enamel-organ. 
This is not visible in fig. 22, since the plane of that section 
passes altogether beneath m+. Fig. 25, however, represents a 
section taken at a higher plane, where the extreme upper or 
basal portion of dp2 is cut through, along with its associated 
residual lamina (rdl.). The latter is seen to be continued 
backwards into the first molar, and the lower face of the 
enamel-organ of this tooth (m+) is seen to be shaved through. 
Fig. 26 shows a still higher plane, where therefore the con- 
tinuity with the lamina in the premolar region is not visible, 
but where the lamina (m2 dl.), ascending posteriorly, and 
becoming freed from the hinder part of the developing tooth, 
is continued backwards into the region of the future second 
molar. Here the first molar is seen to be a deeply indented 
(“glockenformig”) enamel-organ (cf. fig. 27), which in its 
degree of maturity now rivals dp. It will be remembered 
that in the preceding stage the enamel-organ of m+ had only 
