288 



ANATOMY OF VERTEBRATES. 



Dentition of Perameles. 



The Bandicoots which approach nearest to the Myrmecobius in 

 the condition of the incisive and canine teeth, are the Perameles 

 obesula and P. Gunnii. There is a slight interval between the first 

 and second incisor, and the outer or fifth incisor of the upper jaw 

 is separated from the rest by an interspace equal to twice its own 

 breadth, and moreover presents the triangular pointed canine-like 

 crown which characterises all the incisors of Myrmecobius ; but the 



four anterior incisors are 

 placed close together and 

 have compressed, quad- 

 rate, true incisive crowns. 

 From these incisors the 

 canine is very remote, 

 the interspace being 

 equally divided by the 

 fifth pointed incisor, 

 which the canine very 

 slightly exceeds in size. In Peram. nasuta, fig. 226, the incisors 

 present the same general condition, but the canines are relatively 

 larger. 



The dental formula of the genus Didelphys is — 



. 5.5 1.1 3.3 4.4 



l 4^ ;c n^3^ ;m 4^= 50 ' fi s- 227 - 



The Opossums resemble in their dentition the Bandicoots more 

 227 than the Dasyures ; 



j \ but they closely re- 



\s C-^0^y^_ \^ /^~-H sem ble the latter in 



W 3 ^ f J^ivi !1 C>>^ 1 ^^^^ 7 tn e tuberculous struc- 



ture of the molars; the 

 two middle incisors of 

 the upper jaw are more 

 produced than the 

 others, from which they 

 are also separated by a short interspace. The canines still exhibit 

 a superior development in both jaws adapted for the destruction 

 of living prey, but the molars have a conformation different from 

 that which characterises the true flesh-feeders, and the Opossums 

 consequently subsist on a mixed diet, or prey upon the lower or- 

 ganised animals. 



The smaller species of Didelphys, which are the most nu- 

 merous, fulfil in South America the office of the insectivorous 

 Shrews of the old continent. The larger Opossums resemble 

 in their habits, as in their dentition, the carnivorous Dasyures, 



\k®^ 



Dentition of Opossum. (Didelphys) 



