MAMMALIA, 503 



Distribution. — The Family of the Opossums is found 

 extending throughout the American continent, except the 

 extreme north. The other three families are found in 

 Australia or the Australian district, including Tasmania and 

 New Guinea. 



This present-day distribution of Polyprotodontia differs 

 from that of the past. There are a large number of meso- 

 zoic mammals found widely scattered in Britain, Europe, 

 United States and elsewhere, which, mainly in their 

 dental character, seem to resemble the modern Polyproto- 

 dontia (especially Myrmecobius). These appear to indicate 

 that the distribution of the Polyprotodontia was in these early 

 times much wider than at present {cf, Diprotodontia), 



Fig. 348. — Inner View of Left Ramus of Lower Jaw 

 OF Amphilestes Broderipi. 



(From Flower and Lyddeker, after Owex.) 



From the Stonesfield Slate. 



Order II. — Diprotodontia. 



The Diprotodontia are essentially herbivorous, and hence 

 they have few chisel-shaped incisors, never exceeding \ 

 and in some cases being reduced to \. The incisors 

 of the lower jaw never exceed one pair, hence the name of 

 the order. The lower canines are always lost, and often the 

 upper molars have not the sharp cusps of the Polyproto- 

 dontia but have blunt tubercles more suited for crushing 

 vegetable food. The limbs vary in character, but they 

 always have the syndactylic hind -foot described in the 

 kangaroo. (This feature is also found in the Peramelidce.) 



P'amily I. — Macropodidae. — A large family of kangaroos and 

 their allies. The kangaroo has been used as a type of metatherian 

 skeleton. The hind-limbs and tail are enormously developed for 



