556 J. T. WILSON AND J. P. HILM. 
in the other forms referred to, but to an even greater extent, 
the suppression has affected the milk dentition and not the 
successional, and that we may extend to Marsupials generally 
the conclusion of Rose, that “‘ Phascolomys Wombat ganz 
ahnlich wie die placentalen Sauger zwei typische gesonderte 
Dentitionen besitzt 7 (11, p. 745). 
In a paper upon the milk dentition of the Rodentia (18) 
Woodward has discussed the occurrence of vestigial teeth 
in certain members of that order, and has shown that, in the 
forms dealt with, these vestigial teeth are representatives of 
the milk dentition. It may be noted that this conclusion is 
reached in the case of the mouse in spite of the fact that 
‘there is present at one stage in the development of the large 
lower incisors a slight downward prolongation of the dental 
lamina on the posterior side of the enamel-organ of that tooth.” 
This is, of course, simply a repetition of the ordinary mar- 
supial condition. Upon it he comments :—‘‘ This might be 
regarded as presenting an indication of a permanent tooth, the 
large incisor being referred to the milk dentition, while the 
vestigial incisor in front might represent the pre-milk dentition. 
On the other hand, if this very slight prolongation of the 
dental lamina has any morphological value at all, I should be 
inclined rather to consider that it represented that supposed 
fourth dentition, as described by Kiikenthal and Leche for the 
Seals” (p. 626). Here, then, we find Woodward applying 
to the vestigial teeth of the mouse precisely that mode of 
interpretation which is claimed by us to be alone capable of 
affording a satisfactory solution of the marsupial problem. 
In Kikenthal’s latest utterances (in reply to Leche) upon 
the problems of the mammalian dentition (27) we have a con- 
venient summary of his views, which have undergone little if 
any change from those of his earlier papers. 
He adheres firmly to the view that both the ordinary denti- 
tions of mammals were inherited from sub-mammalian ances- 
tors, but apparently admits as established the assertion that 
“traces of two other extinct dentitions are occasionally still 
present embryonically.” 
