678 BERTHA E. MARTIN 



finally on the periphery, a connective tissue capsule. The rest 

 of these nodules is entirely epithelial, having a ''central cellular 

 core inclosed by concentrically arranged flattened cells forming 

 a compact zone." The authors interpret these 'nodules' as the 

 vestigial remains of an earlier dentition. They arise "by 

 structural differentiation of the labial aspect of the enamel 

 organ, and occur only in those regions of the lamina which con- 

 stitute the enamel organs of the future teeth. " Over lying teeth 

 which are about to erupt, Wilson and Hill also found in Pera- 

 meles sporadic cases of nodules composed of concentrically 

 arranged epithelial cells. 



Marrett Tims describes similar structures overlying the first 

 premaxilla and second molar of the guinea-pig, and interprets 

 them as representing the last vestigial remains of the milk den- 

 tition. A spherical body composed of "concentrically arranged 

 epithelial cells" has been found by Tims in connection with the 

 last premolar of the dog, and bj^ Woodward in connection with 

 the last premolar of Gymnura. Tims believes there is thus es- 

 tablished a graded series in degenerating teeth. He recalls the 

 fact that Woodward has figured a "calcified vestigial incisor in 

 the mouse which, in cross section, appears as a narrow^ loop of 

 dentine forming three-quarters of a circle and bordered by cells 

 of the enamel organ." Tims says that it is not hard to imagine 

 that a still further stage of degeneration would give rise to a 

 stage like that seen in the dog, guinea-pig, and Gymnura. 



In the lower jaw" of the edentate, Manis javanica, Tims has 

 also described and figured a downward growth of the oral epi- 

 thelium which he has interpreted as representing a tooth vestige. 

 In some sections this downgrowth lies in the underlying tissue 

 unconnected with the oral epithelium. In the figures these 

 structures look exactly like the first stages in the formation of 

 the cysts in the upper jaw of Dasypus. 



I believe that these cysts occurring in the upper jaw of D. 

 novemcinctus represent tooth vestiges. My reasons are as fol- 

 lows : 



1. They always occur in the same place, — the extreme pos- 

 terior end of the premaxilla. They are found in the same relation 

 to the dental ridge as are the germs of the functional back teeth. 



