MARSUPIALS. 383 



the difference in the number of teeth between the Phalanger and 

 the Opossum resolves itself into the former being minus certain 

 incisors in the upper and lower jaws, the great development of the 

 lower incisor producing an atrophy of all the rest. 



The interspace between the functionally developed incisors and 

 molars in both jaws always in the Phalangers contains teeth of 

 small size, of little apparent use, and variable not only in their 

 proportions but their number. 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 premolars jf-Jt separated by the 

 dotted line from the true molars in figs. 1 and 2, PI. 100, 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 Phal. Cookii, (fig. 2) and 

 as in the great flying Phalanger {Petaurus 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 incisors, we may find three teeth, as 

 in Phal. Cookii and Phal. cavifrons ; or there may be only two 

 teeth, the first representing the canine, as in Phal. ursina and Phal, 

 vulpina (fig 1), and the species 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 ; thus, there may be between the procumbent 

 incisors and the posterior premolar either three teeth, as in Phal. 

 Cookii and Phal. cavifrons ; or two, as in Phal. ursina, Phal. maculata^ 

 Phal. chrysorrhoos ; or finally one, as in Phal. vulpina and Phal. 

 fuliginosa. The most important modification is presented by the 

 little Phal. gliriformis of Bell (PL 100, fig. 3), which has only three 

 true molars (m) on each side of each jaw, and has the last and penul- 

 timate premolars below shaped like canines. 



The Phalangers, being provided with hinder hands and pre- 

 hensile tails, are strictly arboreal animals, and have a close external 

 resemblance to the Opossums, by which name they are generally 

 known in Australia and the Islands of the Indian Archipelago, where 



