of the Tooth-Rudiments in Rodents, 313 



with the surrounding mesoderm, though it is true not in the 

 simple manner which is seen in fig. 1. In larger rabbits the 

 size of the rudimentary tooth appears decidedly diminished, 

 as though it were in process of absorption. In still later 

 stages I could no longer find any trace of it, although I am 

 unable to make any precise statement as to the manner of its 

 disappearance, any more than Chabry and Pouchet were able 

 to do. 



In the premaxilla the changes are precisely similar to those 

 in the lower jaw. A strong sunken epithelial wall is formed, 

 which indicates the region of the subsequent cleft between the 

 two halves of the lip and the anterior end of the jaw. It 

 consequently appears simple in the foremost sections, and 

 bifurcate further back. One half of it is to be seen in fig. 2, 

 and a longitudinal section in the combination-picture shown 

 in fig. 3. In this enormous epithelial mass the anterior step 

 on the roof of the oral cavity, as described above in the 

 younger stage, completely disappears. On the inside of the 

 lateral tip of this epithelial mass is situated, as is shown in 

 fig. 2, the enamel-organ of the rudimentary tooth (fig. 2 

 belonged to a series tlirough the head of a rabbit embryo 

 measuring 5*1 centim. in all and 2'3 centim. in cephalic 

 length). The enamel-organ of the first incisor develops into 

 a huge bell, which is open behind, and, in accordance with the 

 conditions previously described {cf. figs. 2 and 13), the rudi- 

 mentary tooth now appears to lie in the cord connecting this 

 bell with the mur plongemit. Owing to the development of 

 the mur phngeant the tip of the tooth has naturally pene- 

 trated very deep down. The combination-picture fig. 3, 

 which is constructed from longitudinal sections through the 

 head of a rabbit embryo of the same size as that of fig. 2, 

 shows these conditions perhaps most distinctly. 



The histological conditions of the rudimentary tooth may 

 be recognized in fig. 2 ; its dentine casing appears broken 

 through on the outside in this figure. The connexion between 

 the pulp and the mesoderm takes place through this breach, 

 not directly however, but in a vei-y complicated fashion, since 

 the enamel-organ appears as if cleft by strands of connective 

 tissue, producing conditions of which the detailed description 

 belongs to another place. In the same way I have no inten- 

 tion of entering into a discussion of the histological conditions 

 in the enamel-organ of the large incisor. 1 would merely 

 refer the reader once more to fig. 2, which in some degree 

 exhibits the peculiar penetration of vascular outgrowths nito 

 the outer wall of the enamel-organ, which has already been 

 dealt with by so many investigators. The rudimentary tooth 



