306 Herr Paul Freund on the Development 



abundance of teetli is not found to be realized in any recent 

 or known fossil form. 



The question now arises as to how far traces of the process 

 of reduction, and remnants of the teeth which have disap- 

 peared, still admit of embryological demonstration in the case 

 of the Kodents. 



This query naturally further divides itself i:ito three in the 

 following manner, each of which questions must be separately 

 investigated for the upper and lower jaw : — 



(1) Since, with the exception of the premaxilla of the 

 Leporidffi (in which two teeth are present), the recent 

 Rodentia possess only one incisor, we are confronted with the 

 question whether vestiges of the other incisors which have 

 disappeared are traceable in the embryo. Herein, especially 

 in connexion with the views of Cope which have been men- 

 tioned above, regard must be paid to the position of possible 

 embryonic rudiments with reference to the large incisor. Are 

 the rudiments situated on the inside or outside of the latter? 

 And is this consequently to be considered as ^. 1 or as i. 2 ? 



(2) Do vestiges of tooth-rudiments exist in the diastema ? 

 This question divides itself, according to the three stages 

 which are observable in the embryonic development of teeth, 

 into three subquestions : — 



(o) Do we find only a dental fold (Zahnleiste) in the 

 diastema ? 



(i) If such a structure is present, are enamel-organs formed 

 upon it ? 



(c) Is enamel produced within the enamel-organs, and 

 dentine by the papillse ? 



In the event of (5) and (c) being answered in the affirma- 

 tive, this supplementary question arises : 



Are the tooth-rudiments which are observed connected with 

 the incisors or the premolars, or do both conditions occur ? 



(3) Since in the Rodent series the number of the molars 

 descends from 6 (in the upper jaw of Lepus) to 3 in the case 

 of the Murida3 (in Hijdromys even to 2), in forms with a 

 reduced number a search would also have to be made for 

 remnants of the molars which have been lost. It is clear that 

 this task may partly coincide with one subdivison of the fore- 

 going question (rudiment at the posterior end of the diastema). 

 I wish to mention at once that in the present paper I have 

 not devoted any special attention to this third question. 

 Since the development of the molars in the Muridaj has been 

 closely studied by Malm under Fleischmann's direction, and 

 since that author says nothing about rudiments of the vanished 

 molars, which certainly would not have escaped his notice, 



