108 THE MAMMALIA. 



delcben's recent observations on the structure of 

 the tarsus or root of the foot in mammals and in 

 Man, 1 the Didelphidae herein show most agreement 

 with the Lower Vertebrates. All the American 

 Marsupials (the number of which has been con- 

 siderably increased by the researches of Hensel, who 

 died at too early an age) possess the determining 

 bones which, it is true, are not altogether wanting 

 in the Australian species, but are very much modi- 

 fied, and thus point to a later differentiation. All 

 of the American species, says Bardeleben, are five- 

 toed. The larger forms, also those without the 

 isolated bony intermedium, and finally those with 

 a reduced metatarsus, are all found in Australia. 

 For this reason Bardeleben thinks himself justified 

 in maintaining it to be probable that America, and 

 not Australia, was the primeval home of the Mar- 

 supials. Hence, that the Australian Marsupials 

 differentiated after the continent became separated 

 from the rest of the earth, and that they there be- 

 came to a certain extent fixed forms. 



If the enormous area of the Australian con- 

 tinent of which Tasmania, New Zealand, and New 



1 Bardeleben, ' Ueber das intermedium tarsi ' (Sitzungsbe- 

 richte der Jenaischen GesellscJiaft fur Medicin und Naturwissen- 

 schaft, 1883). 



