458 Opposable Power of the Thumb. 



all are equally omnivorous. The Phalangers and Petaurists, 

 indeed, display so decided a preference for live birds, as to 

 make it probable that these constitute a main portion of their 

 food in a state of nature ; whilst the Opossums, as it is well 

 known, thrive equally well upon fruit and vegetables as upon 

 flesh, and feed indifferently upon either. 



Nor are the modifications of dentition proper to the Opos- 

 sums and Phalangers, respectively, so very different in reality 

 as they appear to be at first sight. The Opossums have ten 

 incisors in the upper and eight in the lower jaw, canines of 

 the usual form and number, and seven molars throughout, of 

 which four only are true molars, and have flat crowns with 

 blunt tubercles, like the Simise and Lemuridae : the Phalangers 

 and Petaurists, on the contrary, have only six incisor teeth 

 in the upper jaw, and two in the lower; the latter long and 

 procumbent, and both separated from the true molars by a 

 vacant space containing two insulated false molars, generally 

 rudimentary, but sometimes developed to such an extent as 

 to present the appearance and exercise the functions of real 

 canines. In some species, these anomalous canines are in con- 

 tiguity with the lateral incisors of the upper jaw, and are in 

 all cases situated upon the suture connecting the maxillary 

 and intermaxillary bones ; in other instances, the inferior false 

 molars, though rudimentary, are contiguous to the long pro- 

 cumbent incisors, and inclined in the same direction ; so that 

 these teeth may be considered, without impropriety, as lateral 

 incisors in both the upper and lower jaws; a view which greatly 

 diminishes the apparent dissimilarity between the dental 

 systems of the Phalangers and Opossums. The molar teeth 

 of these two genera are still more closely allied in form, being 

 equally provided with flat crowns and blunt tubercles ; only 

 that those of the Phalangers approach more nearly to the 

 molars of the Simiae, both in form and number, than those of 

 the Opossums. Still it is unquestionable that a considerable 

 hiatus does exist between these two systems of dentition ; and, 

 though it might appear in some degree to be filled up by the 

 Dasyures, yet more influential parts of their structure exclude 

 that genus from the present group. At all events, whatever 

 difference may exist in the organs of mastication, between the 

 extreme genera which I have associated in this family, there 

 is, as it has been already observed, but little difference of func- 

 tion, and the natural habits and appetites are nearly the same 

 in all. 



But there are other and very influential parts of the organic 

 structure of these animals, in which the chain of affinities is 

 less broken, and more easily recognised, than in their dental 



