324 IIciT Paul Frciuul on the Development 



successor, whicli in some other way at any rate also stand in 

 closer relation one to another, should under the special con- 

 ditions in question (especially great and therefore also more 

 rapid development of the permanent tooth) fuse together, than 

 that two tooth-germs situated one behind the other, wiiich 

 have otherwise nothing whatever to do with one another, 

 should enter into intimate mutual relations of this kind. 

 Another telling point is tliat the rudimentary tooth and the 

 incisor lie togetlier not only in an alveolus, but also, as may 

 be seen with especial distinctness in tlie case of the squirrel, 

 in one tooth-sac of connective tissue. I do not wish to attach 

 too great weight to the relative position of the tooth-germs. 

 It is true that the rudimentary tooth lies in front of the 

 incisor, but the deciduous i. 2, which we must yet certainly 

 regard as a milk-tooth, also lies, at least according ^to the 

 representation of MM. Chabry and Pouchet, in front of the 

 germ of the second permanent tooth. This is connected with 

 the peculiar conditions of space in the jaws of Rodents. It 

 appears to me to be of more importance that in the squirrel, 

 in wdiich the conditions in question seem to be to a certain 

 extent less abnormal than in the rabbit, the enamel-germs of 

 the rudimentary and permanent tooth are connected together 

 by their " necks " (and this both in tlie upper as well as in 

 the lower jaw) precisely as this is usually described for the 

 milk-tooth and its successor. Altogether I am personally 

 more inclined to the view that the rudimentary tooth is to he 

 considered as the rudiment of a precursor of the large incisor 

 in j/rocess of active degeneration, though I am ready to admit 

 that this can by no means be regarded as finally established. 

 It may further be specially pointed out that in Sciurus, which 

 in many respects has proved even more conservative than 

 Lepus, no distinct trace could be discovered of /. 2, which 

 Lepus has preserved in the shape of tlie milk-tooth and its 

 successor. It will be sliown later on that the anterior of the 

 two enamel-organs, whicli I liave jMoved to exist near the 

 orifices of Stenson's canals, can only with difficulty be regarded 

 as i. 2. Further investigations will have to determine 

 whether the rudimentary teeth, as they appear in the stage of 

 Sciitrus examined by me, have exactly arrived at the height 

 of their development, whether they develop still furtiier, or, 

 lastly, whether they are not perhaps already in ])rocess of 

 degeneration. 



(2) In the Rodents examined are germs of teeth found in 

 the diastema ? To this our discoveries enable us to reply : — 

 }n Lf/'?/.s a well-developed dental fold is found throughout the 



