732 



s(ichical dentition, i.e. the milk-dentition of the Monodelphians. It 

 may Ite stated at once that tlie same holds for the first molar of 

 the npper jaw set of Perameles. 



It is easier to prove the correctness of this view for the lower 

 than for the upper jaw. Following up the Anlage of the tooth-germ 

 of the first molar in the lower jaw, it is clear that it does not 

 evoKe from the free border of the dental lamina, but from the 

 labial wall, contrary to the second molar which is formed indeed 

 as an endostichical tooth from the free border of the dental lamina. But 

 in the lower jaw a more definite proof may i)e given, namely: 

 Following up the Anlage of MI — i.e. tooth 7 — in the lower 

 jaw, one finds that very shortly before the posterior edge of this 

 Anlage the free end of the teeth-band produces a rudimentary tooth- 

 Anlage. This is indicated in fig. 2 by /, and in fig. 7 sections of 





»-..<-5 



Fie. 7. 



it on the right and left side of the jaw are drawn. The Aidage of 

 these rudimentary germs puts the exostichical nature of the first 

 molar beyond doubt. If these germs developed further- also tooth 7 

 would be expelled, as is in reality the case with tooth 6. 



The first molar in the upper jaw has been said to belong also to 

 the exosfichos. Here however I have found no trace of the corre- 

 s|)onding endostichical tooth. And the proof can here only be given 

 by a comparison of the topographical relation of the germs of the 

 first and second molar in regard to the dental lamina. Therefore in 

 fig. 58 thirteen sections are given of the Anlage of the first molar 

 and in fig. 9 of the second molar of the upper jaw. Especially for 

 those who are acquainted with the evolution of the reptilian dentition 



