5384 J. T. WILSON AND J. P. HILL. 
of the undifferentiated dental lamina before and behind, which, 
in turn, is continued into the residual lamin of £ and of p?. 
(We have carefully verified the planes of section, and have 
definitely determined that they correspond to the free portion 
of the epithelial [residual laminar] downgrowth. But, indeed, 
the view here expressed is supported by the whole body of our 
observations.) 
The merest glance at our figure will serve to show that, at 
least in this region, the term ‘‘ bud-like ” applied to the resi- 
dual laminar downgrowth is ludicrously inappropriate. The 
swollen “ bud-like ” outline seen on cross-section is due to a 
general and continuous thickening of the free marginal portion 
of the lamina. 
It may with justice be contended that a perfectly similar 
marginal thickening of the primary dental lamina may be 
noticed prior to the differentiation from it of the earliest 
enamel-organs (though then the whole structure is much fuller 
and plumper than is the residual lamina of later stages), and 
that the later recurrence of such a condition may well be taken 
as heralding the advent of a new dentitional series. To this 
we reply that that general and continuous marginal thickening 
of the lamina, primary or residual, of itself signifies 
nothing at all in the way of tooth differentiation. 
It is possible, indeed, to affirm—but this is equally true of a 
non-swollen residual dental lamina destitute of any tooth-sac— 
that the epithelial residuum is the potential equivalent of 
further successional teeth. But in our view there is no more 
reason to identify the residual dental lamina with any one tooth 
generation than there is to identify the primary and undifferen- 
tiated dental lamina of a higher mammal specifically with the 
“milk,” to the exclusion of the “‘ permanent ”’ series of mam- 
malian teeth. 
We regard the lingually placed ‘epithelial downgrowths ” 
beside the normal adult enamel-organs merely as portions of a 
dental lamina not yet wholly exhausted of its formative acti- 
vity, and therefore possibly still capable, exceptionally, of 
providing material for the production of teeth homolo- 
