340 



on each side, each heset 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 correspond- 

 ing anterior premolar in the Opossum, by a short interval from those behind. 



The canine tooth but slightly exceeds in size the above premolar, and consequently here 

 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, the corresponding tooth presents more of the proportions and form of a true 

 canine. 



The incisors, which are most variable in number in the Carnivorous section of the order, 

 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. The lower jaw has but two large procumbent in- 

 cisors, as in all the vegetable-eating Marsupials. 



In the lower jaw there is the same number of molars and functional premolars as in the 

 Opossums ; the two very minute and functionless molars, which form part of the same con- 

 tinuous series, represent the small premolars of the upper jaw ; and anterior to these there is 

 one very small canine and one very large and procumbent incisor on each side. 



The interspace between the functionally developed incisors and molars in both jaws always 

 contains in the Phalangers teeth of small size and little functional importance, and variable 

 not only in their proportions but their number. 



The constant teeth in the Phalangers are the ~ true molars, and the ^ incisors. 



The canines are constant in regard to their presence, but variable in size ; they are always 

 very small in the lower jaw. 



With respect to the functional premdlars |^, these are always in contact with the molars, 

 and their crowns reach to the same grinding level ; sometimes a second premolar is similarly 

 developed in the upper jaw, as in the Ph. Cookii, and as in the great flying Phalangers (Pet. 

 Taguanoides), but it is commonly absent, or replaced by a very minute tooth, shaped like a 

 canine ; so that in the upper jaw, between' the posterior or functional premolar and the in- 

 cisors, we may find three teeth, of which the posterior is the largest, as in Ph. Cookii, or the 

 smallest, as in Ph. cavifrons ; or there may be only two teeth, as in Ph. ursina and Ph. vul- 

 pina, and the species, whatever that may be, which M. Fr. Cuvier has selected as the type 

 of the dentition of the genus. 



In the lower jaw similar varieties occur in these small and unimportant teeth ; e. g. there 

 may be between the procumbent incisors and the posterior premolar, either three teeth, as in 

 Ph. Cookii and PA. cavifront, or two, as in Ph. ursina, Ph. maculata, and Ph. chrysorrhoos ; 

 or, finally, one, as in Ph. vulpina and Ph.fuliginosa. The most important modification is 

 presented by the little Ph. gliriformis of Bell, which has only three true molars on each side 

 of each jaw. As these modifications of the teeth are unaccompanied by any change of 

 general structure or of habit, whilst those teeth which most influence the diet are constant, 



