DIDELPHYIDsE 



133 



(3. Teeth rooted. Three upper incisors and a canine. Hind 

 limbs not disproportionately large. Feet syndactylous, 

 broad, with four subequal outer toes, and a large 

 opposable hallux. Phalangeridce. 



y. Teeth rooted. Three upper incisors, and frequently a 

 canine. Hind limbs disproportionately large, with 

 syndactylous feet as in Peramelidce. Macropodidce. 



Suborder POLYPROTODONTIA. 



The leading characters of this group are given in the foregoing 

 schedule. This group is the only one represented at the present 

 day, and so far as we know also in past epochs, beyond the confines 

 of the Australasian region and adjacent islands. 



Family DIDELPHYID^E. 



Dentition : i --, c ^, p ^ , m % ; total 50. Incisors very small 

 and pointed. Canines large. Premolars with compressed pointed 

 crowns. Molars with numerous sharp cusps. The last premolar 

 preceded by a deciduous multicuspidate milk-molar, which remains in 

 place until the animal is nearly adult (Fig. 34). Limbs of moderate 

 development, each with five complete and distinct toes, all of which 

 are provided with short, compressed, 

 curved, sharp claws of nearly equal 

 size, except the first toe of the hind 

 foot or hallux (Fig. 37), which is large, 

 widely separable from the others, to 

 which it is opposed in climbing, and 

 terminates in a dilated rounded ex- 

 tremity, without a nail. Tail gener- 

 ally long, partially naked and prehen- 

 sile. Stomach simple. Caecum of 

 small or moderate size. Pouch gener- 

 ally absent, sometimes represented by 

 two lateral folds of the abdominal 

 integument, partially covering the 

 teats, rarely complete. Vertebrae : 

 C 7, D 13, L 6, S 2, C 19-35. 



The Didelphyidce, or true Opos- 

 sums, differ from all other existing 

 Marsupials in their habitat, being 

 peculiar to the American continent. 

 They are mostly carnivorous or insectivorous in their diet, and 

 arboreal in habits. 



Opossums occur throughout the greater part of the American 



FIG. 37. Skeleton of the right hind 

 foot of the Virginian Opossum (Didelphys 

 marsupialis). 



