543 



Erinaceus. Recently Hoffmann (13) has stated his belief that the 

 Ungulate molars belong to the milk series; I have not examined 

 sections of the jaws of Ungulates, but if a similar condition be pre- 

 sent in them as is found in the Dog, it is possible he might have 

 arrived at this conclusion from the fact that the molars develope from 

 the outer of the two downgrowths of the dental lamina. 



Again, from the smaller size of the second molar and from a com- 

 parison of these teeth in other members of the Canidse, as well as 

 in man and other animals, we must believe that this tooth is also 

 undergoing suppression ; and yet, there is no evidence of any re-ap- 

 pearance of the pre -milk dentition, such as I assumed may have taken 

 place in the case of ^m^ 



I would remark in passing that it might be urged that the den- 

 tal lamina figured in connection with ^* (fig. 4) may not represent 

 the post - permanent series, but may be the turning in of the dental 

 lamina at the posterior end due to shortening of the jaw. Such I do 

 not believe to be the case, for it is most marked about the centre of 

 the tooth, and does not extend backwards as far as the tooth itself; 

 and, moreover, the dental lamina is continued directly backwards for 

 a short distance behind the second molar. 



From these considerations certain conclusions may, I think, be 

 drawn. 



1) That there is not sufficient evidence for believing in the exist- 

 ence of a pre -milk dentition, even in a rudimentary condition, in the 

 Mammalia of the present day. 



2) That suppression of the dentitions is probably taking place 

 from without inwards ^ the lingual downgrowth of the dental lamina, 

 which 1 take to represent the post -permanent series, occasionally de- 

 veloping into a functional tooth thereby giving rise to an additional 

 third functional tooth as sometimes occurs in Man (14); and, I be- 

 lieve, accounting in some cases for the successor to dpm^. 



In any case, the formerly vexed question as to which is the older 

 and which the super -added dentition once more disappears, as both 

 are of equal antiquity, handed down from reptilian ancestors. 



3) That in the Dog, the first premolar and the molars belong to 

 the so-called permanent dentition. 



If these view be accepted the teeth of the Marsupials would, once 

 more, appear to belong to the permanent series. 



It is a well known fact that in the upper jaw of the Dog, the 

 characters of the last deciduous pre-molar are almost identical with 

 those of the first true molar, and those of the penultimate deciduous 

 pre-molar with those of the fourth pre-molar. 



