422 DEVELOPMENT OF ORGAlfS IN MAMMALIA. [XII. 



which according to most authors give rise to the enamel 

 and dentine respectively. 



The proctodseuin. The cloacal section of the ali- 

 mentary canal is placed in communication with the 

 exterior by means of a shallow epiblastic invagination 

 constituting the proctodseum. 



