316 Herr Paul Freund on the Development 



end, so that a small cone is attached to the oral epithelium, 

 followed by connective tissue, in the arrangement of the cells 

 of which we can still frequently trace the direction of the 

 epithelial cord which has disappeared. Deep down we then 

 see the severed thickened end as a circle filled with epithelial 

 cells, which is distinguished by the fact that, like other 

 epithelial remnants undergoing degeneration in the same way, 

 it takes up carmine very freely, and consequently appears of 

 a dark red colour. It is clear that this process is the same as 

 that also undergone by the dental fold in mammals with a 

 complete dentition, after the enamel-organs have been formed 

 and constricted off from it. The dental fold in the diastema 

 of the rabbit, however, perishes without ever having produced 

 enamel-organs. In an embryo rabbit 23 millim. in cephalic 

 and 51 millim. in total length every trace of the fold has 

 disappeared in the anterior portion of the diastema ; but in 

 the posterior portion, on the contrary, in the neighbourhood 

 of the molars, there appears in each section at the same spot 

 in the connective tissue of the palate a small red circle, which 

 I am inclined to regard as the last vestige of the dental fold. 

 My reasons for doing so are the following : — In the first place, 

 it is found in the posterior portion of the diastema in every 

 section at the same spot, and this spot, so far as I can see, 

 corresponds to that at which the epithelial fold is found in 

 younger stages. Secondly, in the connective tissue there 

 frequently proceeds from the red spot to the oral epithelium 

 a kind of cord of cicatricial tissue, i. e, a clear streak, in which 

 we find but few nuclei, or none at all, while at the edges of it 

 the nuclei are closely packed. Thirdly, the epithelial circle 

 can be traced as far as the dental fold of the first premolar, 

 though I am unable to assert with absolute certainty that a 

 direct connexion exists. If my interpretation is correct, it 

 would result therefrom, that the dental fold in the diastema 

 in the rabbit disappears from in front backwards. 



With regard to the rudiments of the molars in Lepus cuni- 

 culus, I have no special statement to make. In fig. 13 we see 

 only three, and tiiese still in a very undeveloped condition : 

 the enamel-organs have the shape of flat shells. Another 

 model, which is not figured here (prepared from a series of 

 longitudinal sections through the head of a rabbit embryo 

 2'3centim. in cephalic and 5*1 centim. in total length), shows 

 the rudiments of five molars. In the second and third we 

 find the characteristic bell-shape, with the projections directed 

 towards the pulp. Nos. 1 and 4 are less developed ; the fifth 

 rudiment appears in the form of a button-shaped epithelial 

 thickening, with only quite a shallow depression, at the 

 posterior end of the dental fold. 



