II.] MARSUPIALS. 35 



their diet, the incisor teeth are numerous and pointed, the canines 

 are large and well developed, and the whole of the anterior teeth 

 form a series more or less nearly continuous with those on the 

 sides of the jaws. The typical diprotodonts, or those in which 

 two of the toes of the hind foot are enclosed in a common integu- 

 ment 1 , are exclusively confined to the Notogaeic realm, where they 

 attain their maximum development in the Australian region ; but 

 the polyprotodonts and an aberrant group of diprotodonts are 

 still represented in the Neogaeic realm, while during the Secondary 

 and earlier part of the Tertiary period the former were widely 



FIG. 2. SKULL OF RAT-KANGAROO. 

 (To exhibit Diprotodont type of dentition.} 



spread over Arctogaea. In the Australian region marsupials play 

 the part of the eutherians of other regions, and show a remark- 

 able diversity of external form and structure, adapting them to all 

 modes of life with the exception of the aquatic. And it is fairly 

 evident that within the limits of this region the diprotodonts were 

 originally evolved from the more generalised polyprotodonts. 



Of the three existing family groups into which the Notogaeic di- 

 protodonts are divided the first is the Macropodidce, or the kangaroos 

 and their allies ; this being in some respects the most specialised 

 group of all, and characterised by certain peculiar features in the 

 skull and dentition. Among these the typical genus Macropus, in- 

 cluding the true kangaroos, comprises a total of twenty-three 

 species, out of which twenty are confined to Australia and 



1 The term syndactylous is applied to this type of foot. 



32 



