420 A MANUAL OF DENTAL ANATOMY. 



" Some resemble wolves, others marmots, weasels, squirrels, flying- 

 squirrels, dormice, or jerboas. 



" They are classed in six distinct families, comprising about thirty 

 genera, and subserve most of the purposes in the economy of nature 

 fulfilled in other parts of the world by very different groups ; yet 

 they all possess the common peculiarities of structure and habits 

 which show that they are members of one stock, and have no real 

 affinity with the old-world forms, which they often outwardly 

 resemble." " Geographical Distribution of Animals." p. 391. 



WHAT Mr. Wallace says, speaking of the creatures in their 

 entirety, is equally applicable to their teeth. 



In Australia, the present home of the Marsupials, repre- 

 sentative species abound ; that is to say, widely different 

 though the animals really are, there are many genera and 

 species which have the habits of, and, as it were, fill the 

 place of such creatures as the Carnivora and Insectivora and 

 Rodents amongst the placeutal mammalia. And not only 

 do they possess something of their habits and external con- 

 figuration, but in those characteristic structures which are 

 subservient to the creature's immediate wants, the marsupial 

 representatives closely mimic the more highly organised 

 placental mammals. Thus the teeth of an insect-eating 

 marsupial very closely resemble those of a true Insectivore, 

 though retaining certain eminently marsupial characters ; 

 in the same way the dentition of the marsupial Thylacine 

 mimics that of a dog (compare Figs. 187 and 188). 



And although marsupial dentitions do vary very much, 

 yet there are many transitional forms by which we are some- 

 times able to trace the successive modifications through 

 which extreme divergence has been ultimately attained. 



Just as we ascribe to placental mammals the formula 



as the typical or parent dental formula, so to the Marsupials 

 we must ascribe the following 



.3134 



