of the Tooth-Rudiments in Rodents. 319 



characteristic representation of the posterior of the two rudi- 

 ments (the section also passes through the region of the orifice 

 of the Stenson's canal) : compare for this purpose my fig. 10. 

 But according to the explanation of the figures they interpret 

 the rudiment quite wrongly as that of the large incisor, 

 which, as a glance at the model, fig. 14, will show, is much 

 further developed, and besides this also has quite a different 

 position. 



It now remains for us to make more special observations 

 with reference to certain of the above four paragraphs. 



The dental fold upon which in the lower jaw the enamel- 

 organs of the rudimentary tooth and of the large incisor are 

 situated [cf. for this figs. 6 & Q, and model, fig. 15) proceeds 

 from the commencement of a peculiar mur plongeant, which 

 envelops as a deep case the anterior end of the Meckelian carti- 

 lage together with the superincumbent covering-bone. It is 

 precisely the same formation as that described and figured by 

 Chabry and Pouchet for the rat. Together with the epithe- 

 lium of the oral cavity, it appears in a median transverse 

 section as a closed circular epithelial arch, in the interior of 

 which the dental rudiments^ the bone, and the cartilage are 

 contained. Upon the surface of the mucous membrane of the 

 oral cavity, the spot from which the epithelial fold and be- 

 side it the mu7' plongeant proceed is distinguished by a groove. 

 For posteriorly the epithelial fold ceases to be in continuity 

 with the epithelium of the oral cavity {cf. model, fig. 15). 

 That from the fold an epithelial cord runs backwards for a 

 short distance has already been mentioned^ and may be seen 

 from the model. Now on the outer side of this epithelial fold 

 the enamel-organs of the rudimentary tooth and of the large 

 incisor are attached close together, each by means of a long 

 neck, in such a way that only the somewhat clavate end of 

 the epithelial fold projects a little further downwards and 

 inwards than this point of attachment. For, as is shown both 

 by the figures and the model, the neck of the rudimentary 

 tooth is a particularly elongated structure, which reaches so 

 far downwards and backwards, that the enamel-bell of the 

 rudimentary tooth comes to lie beside the Meckelian cartilage 

 {cf. fig, 6). Neither the neck of this enamel-organ, the 

 stouter and more massive one of the incisor lying behind it, 

 nor lastly also the dental fold itself have smooth outlines ; on 

 the contrary, they are beset with projections and depressions 

 of the most varied kind {cf for this figs, b & Q), so that in 

 many places the appearance presented reminds us of that of 

 the proliferating rudiment of a gland, or still better of that of 

 a carcinoma. 



23* 



