38S MARSUPIALS. 



the upper jaw are small and obtuse ; the two anterior or middle 

 incisors are twice as long, broad, and thick as the posterior incisors ; 

 they are conical, slightly curved, sub- compressed, bevelled off ob- 

 liquely to an anterior cutting edge, but differing essentially from 

 the denies scalprarii of the Rodentia in being closed at the extremity 

 of the fang. The two incisors of the lower jaw resemble those 

 of the upper, but are larger and more compressed ; they are also 

 formed by a temporary pulp, and its absorption is accompanied by 

 a closure of the aperture of the pulp-cavity, as in the upper incisors. 

 The Koala, therefore, in regard to the number, kind, and con- 

 formation of its teeth, closely resembles the Phalangers, with which 

 it also agrees in its long coecum and the general conformation of 

 its digestive organs. It has also the extremities similarly organised 

 for prehension ; each is terminated by five digits ; the hind feet 

 are provided with a large thumb, and have the two contiguous digits 

 enveloped in the same tegumentary fold ; the anterior digits are 

 divided into two groups ; the thumb and index being opposed to the 

 other three fingers. We have already noticed a structure approaching 

 to this in some of the small Phalangers. The Koala, however, 

 differs from the Phalangers and Petaurists in the extreme shortness 

 of its tail, and in its more compact and heavy general form. It is 

 only known to feed on the buds and leaves of the trees in which it 

 habitually resides. 



1.53. Poephaga. — The present tribe includes the most strictly 

 vegetable feeders in the Marsupial order ; all the species have a com- 

 plex sacculated stomach, and a long simple coecum. 



Genus Hypsiprymnus, Potoroos. — Guided by the modifications of 

 the teeth we pass from the Koala to the Potoroos and Kangaroos 

 — animals of widely different general form. The Potoroos, however, 

 present absolutely the same dentition as does the Koala, some slight 

 modifications in the form of certain teeth excepted. The premolars 

 (PI. 100, fig. 7,p) 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 



