34 
EDWARD B. POULTON. 
caustic potash, after the bone had been softened in dilute 
nitric acid, the papillae had been accidentally drawn out of 
their tubes in the epithelium (by the partial separation of the 
plates), so that their shape was peculiarly distinct. In many 
parts of the sections these papillae formed a fringe along the 
surface of the subepithelial tissues. 
Probable Relation of the Posterior Horny Plates 
to the True Teeth. — The anterior plates are omitted from 
this consideration because there is as yet no evidence of the 
occurrence of teeth beneath them. No epithelial thickening or 
any other indication of their presence could be made out in Dr. 
Parker’s sections. Certain facts, however, seeem to prove that 
there is some relation between the posterior plates and the true 
teeth. These facts are, (1) the lodgment of the plates in the 
alveolar cavity in which the true teeth appear at an earlier 
stage ; (2) the existence of a certain correspondence between 
the divisions of the plates, the compartments of the alveoli, 
and the number of the teeth ; (3) the evidence that the plates 
are developed as at least two separate tubercles, apparently 
corresponding to the two chief true teeth situated beneath 
them ; (4) the rough correspondence between the shape of the 
plates and teeth, the chief and higher cusps being internal 
above and external below, while the chief and higher lateral 
borders of the upper and lower plates have the same position 
respectively. On the other hand, the following facts point in 
an opposite direction : — (1) The possible rudiments of the 
upper plates in Dr. Parker’s sections as epithelial thickenings 
which do not correspond with the position of the true teeth, but 
are anterior and external to the latter ; (2) the occurrence of 
the small third concavity at opposite ends of the upper and 
lower plates, when considered in relation to the true teeth of 
both jaws. 
The first objection may be met by the undoubted fact that 
the position of the upper plates in the adult corresponds to 
the position of the true teeth in the young, and not 
to that of the epithelial thickening. The position of the 
thickening has already been briefly referred to ; it could be 
