382 MARSUPIALS. 



and Perameles of the preceding tribe with the small insectivorous 

 Phalangers. 



Genus Phalangista. — The Phalangers are so called from the 

 phalanges of the second and third digits of the hinder extremity 

 being inclosed in a common sheath of integument and they have 

 the innermost digit modified to answer the purposes of a thumb. 



In the skull of a Phalangista Cookii, of which the dental formula 

 is given in PI. 100, fig. 2, there are both in the upper and lower 

 jaws four true molars on each side, each beset with four three- 

 sided pyramidal sharp-pointed cusps ; thus these essential and most 

 constant teeth correspond in number with those of the Opossum : 

 but in the upper jaw they differ in the absence of the internal 

 cusp, which gives a triangular figure to the grinding surface of the 

 molars in the Opossum ; and the anterior single cusp is wanting 

 in the true molars of the lower jaw. Anterior to the upper 

 grinders in this Phalanger there are two premolars of similar shape 

 and proportions to those in the Opossum ; then a third premolar, 

 too small to be of much functional importance, separated also, 

 like the corresponding anterior premolar in the Opossum, by a 

 short interval from those behind. 



The canine tooth but slightly exceeds in size the contiguous pre- 

 molar, and here consequently occurs the first great difference between 

 the Phalangers and Opossums ; it is, however, but a difference in 

 degree of development ; and in the Ursine and other Phalangers, as 

 well as in the Petaurists (fig. 4), the corresponding tooth presents 

 more of the proportions and form of a true canine. 



The incisors, which we have seen to be most variable in 

 number in the Carnivorous section, are here three instead of five on 

 each side of the upper jaw ; but their size, especially that of the first, 

 compensates for their fewness. 



In the lower jaw there is the same number of molars and 

 functional premolars as in the Opossums ; the three very minute 

 and functionless teeth, which form part of the same continuous 

 series, represent the two small premolars and the canine of the 

 upper jaw ; and anterior to these there is one very large pro- 

 cumbent incisor on each side. From this analysis it appears that 



