16 



three fingers. The fore-paws have a similar structure in some of 

 the small Phalangers ; it is very conspicuous in some of the Petau- 

 rists. The Koala, however, differs from the Phalangers and Petau- 

 rists in the extreme shortness of its tail and in its more compact and 

 hea.vj general foim. It is known to feed on the buds and leaves of 

 the trees in which it habitually resides. 



Tribe IV. POEPHAGA. 



The present tribe includes the most strictly vegetable feeders ; all 

 the species have a complex sacculated stomach and a long simple 

 caecum. 



Guided by the modifications of the teeth we pass from the Koala 

 to the Kangaroo family {Macropodidce) , — animals of widely different 

 general form. The Potoroos, however, in this group, present abso- 

 lutely the same dentition as the Koala, some slight modifications in 

 the form of certain teeth excepted. The spurious molares, in their 

 longitudinal extent, compressed form, and cutting edge, would chiefly 

 distinguish the dentition of the Potoroo, but the Koala evidently 

 offers the transitional structure between the Phalangers and Potoroos 

 in the condition of these teeth, of which one only is retained on each 

 side of each jaw, in both Phascolarctus and Hypsijirymnus. 



The dental formula of the genus Hypsiprymnus is : incisors j^ ; 

 canines ^^ ; prsemolares j^ ; mol. j^ : :=30. 



The two anterior incisors are longer and more curved, the lateral 

 incisors relatively smaller than in the Koala. The pulps of the an- 

 terior incisors are persistent. 



The canines are larger than in the Koala; they always project 

 from the line of the intermaxillary suture ; and while the fang is 

 lodged in the maxillary bone, the crown projects almost wholly from 

 the intermaxillary. In the large Hypsiprymnus ursinus the canines 

 are relatively smaller than in the other PotorooS, a structure which 

 indicates the transition from the Potoroo to the Kangaroo genus. In 

 the skeleton of this species in the Leyden Museum the canines pre- 

 sent a longitudinal groove on the outer side. 



The characteristic form of the trenchant spurious molar has just 

 been alluded to ; its maximum of development is attained in the ar- 

 boreal Potoroos of New Guinea (^Hypsiprymnus ursinus, and Hyps. 

 dorsocephalus) ; in the latter of which its antero- posterior extent 

 nearly equals that of the three succeeding molar teeth. 



In all the Potoroos the trenchant spurious molar is sculptured, 

 especially on the outer side, and in young teeth by many small verti- 

 cal grooves. The true molares each present four three-sided pyrami- 

 dal cusps, but the internal angles of the two opposite cusps are con- 

 tinued into each other across the tooth, forming two concave trans- 

 verse ridges. In the old animal these cusps and ridges disappear, 

 and the grinding surface is worn quite flat. 



In the genus Macropus the normal condition of the permanent 

 teeth may be expressed as follows : — incisors rE^ ; canines ^^ ; prre- 

 raolaresj^; molares jp^ : =28. 



