462 J. T. WILSON AND J. -P.- HILL. 
Stage 11].—P. obesula: mammary feetus. 
Length from vertex to root of tail . . . 22 mm. 
Head length : : ‘ . ~ oe 
Studied in coronal and horizontal series. 
The examination of this stage reveals features of uncommon 
interest and importance. 
Although our specimen representing this stage is not speci- 
fically identical with those of the stages immediately pre- 
ceding and succeeding, we are confident that this difference is 
of no consequence, and does not in the least prejudicially 
affect the conclusions arrived at. So far as it is possible to 
ascertain and to judge, the condition presented by the stage 
answers exactly to what one would expect to find, intermediate 
between Stages 11 and tv. The correspondences, indeed, are 
throughout unmistakable. 
Here for the first time the great majority of the permanent 
teeth are sufficiently differentiated to be recognisable as dis- 
tinct and individual enamel-organs. Most of these, however, 
as we shall see, are in a very early stage of their individual 
differentiation, and are not yet emancipated from the dental 
lamina. The latter structure is relatively massive and abso- 
lutely continuous throughout. Its line of attachment to the 
oral epithelium (proximal margin or “ neck ”) is, however, in 
parts considerably attenuated; and in a few places, for a 
section or so, it is just possible to recognise a discontinuity 
between these structures. This is doubtless due to the com- 
mencement of the process of resorption which Rose has shown 
(9) to produce fenestration of the lamina. 
With these extremely rare and slight interruptions the at- 
tachment to the Malpighian layer extends up to the posterior 
end of the molar part of the lamina. 
Upper Jaw.—In the incisor region the extreme anterior 
end of the dental lamina (fig. 16, d/.) is directed somewhat 
mesially, but it no longer lies so distinctly in a transverse 
direction as in the preceding stage. * 
The Anlage of the first permanent incisor (fig. 16) is indi- 
