DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 485 
hibits a much more advanced condition than does the corre- 
sponding Anlage in the upper jaw. 
The labial portion of mz in turn disappears rather abruptly 
(see fig. 42), leaving a simple elongated dental lamina (dl.). 
The latter has now become separated from the oral epithelium, 
and soon disappears entirely from the section, without having 
given any indication of the future formation of the third molar. 
Stage 1V.—P. nasuta: mammary fetus. 
Length from vertex to root of tail. : . 34mm. 
Head length : : : : oe On sss 
Coronal, horizontal, and sagittal sections examined. 
The transition from Stage 111 to Stage rv represents a greater 
advance in development than that from Stage 11 to Stage 111. 
Upper Jaw.—The dental lamina (fig. 43, di.) begins some 
distance in front of the anterior end of the first incisor, as a 
downgrowth from the lingual angle of a broader epithelial 
invasion of the connective tissue (ca.). The possible signifi- 
cance of this will be adverted to in the sequel. In fig. 44, 74, 
is seen to be connected with the dental lamina by a bridge of 
cells (cd.), or“ Verbindungsbriicke” of Rose. This struc- 
ture alone bears witness to the earlier condition manifested in 
Stage 111, where the enamel-organ of 7+ was still an integral 
portion of the dental lamina. Beyond the attachment of the 
connecting bridge (c.d.) the “ residual” dental lamina (rdi.) 
extends as a free laminar ingrowth. 
Springing from the labial angle of the broad epithelial 
ingrowth above referred to may be seen (fig. 44) a hooked 
cellular process (ep.). And, between this and the proper 
dental lamina itself, the surface of the broad epithelial ridge is 
beset with irregularities. In many sections, indeed (cf. fig. 
46, cp.), completely isolated epithelial cell groups may be seen 
in the connective tissue to the labial side of the “ Verbin- 
dungsbriicke” of z+, i.e. between the latter and the irre- 
gular edge of the broad epithelial mass which forms the basis 
from which the proper dental lamina springs. In other sec- 
