148 J. T. WILSON AND J. P. HILL. 



For these reasons we have uo hesitation in identifying the 

 anterior of the two prominent papillated enamel-organs in 

 the upper and lower jaws of our younger specimen with those 

 developing teeth in the older which we have marked as 

 '' w " and " w " I'espectively. 



In the course of our description of the older stage we have 

 noted the presence of a small cupped and somewhat im- 

 perfectly formed enamel-organ in front of the conical calcified 

 tooth " w." The enamel-organ in question is quite deeply 

 placed and is obviously in series with the more fully developed 

 teeth behind it. We have designated it as " v." Again, in 

 the younger specimen we have shown that there is present, 

 in the precisely corresponding coronal plane, a small and 

 already strongly calcified vestigial tooth (figs. 4 and 5). This 

 actually indents the deep aspect of the mouth epithelium at 

 the labial side of the attachment to the latter of the dental 

 lamina. • This, therefore, cannot be the enamel-organ '' v" 

 of the older specimen. But we have also seen (p. 143) that, 

 in the immediate neighbourhood of this vestigial tooth, the 

 dental lamina is somewhat enlarged and bulbous. It seems 

 tolerably evident that this bulbous enlargement of the 

 adjacent part of the dental lamina must be the genuine 

 representative of the later enamel-organ ("v") (text-fig. 2). 

 We, therefore, hold that this latter tooth-rudiment, " v," 

 must be regarded as the true morphological successor to the 

 small calcified vestigial tooth which is present in our smaller 

 specimen. The latter vestigial tooth we accordingly indicate 

 by the symbol " dv," as being the deciduous predecessor of 

 the enamel-organ " v" of the later stage. 



In the lower jaw of the older specimen no representative 

 of a lower '* v" was met with. But in the younger, as we 

 have already stated, there is found, on one side certainly, 

 and more doubtfully on the other, a structure which, in its 

 situation and its relations to other structures, exactly corre- 

 sponds to the small calcified upper tooth " dv," and thus 

 represents a lower *' dv.'' In the neighbourliood of this 

 vestigial tooth-element the dental lamina is slightly enlarged. 



