84 Vertebrata. 



The wombat is a burrowing and gnawing mar- 

 supial, whose chisel-shaped incisor and other teeth 

 continue permanently to grow, and thus the waste of 

 tooth-tissue which takes place in the process of grind- 

 ing the roots and twigs which constitute its food, is 

 restored. This animal is about 2\ feet long, and, like 

 the koala or native bear of Australia, has an accessory 

 gland in the stomach, and a long caecum or pouch, 

 where the large and small intestines unite. They are 

 both also almost tail-less, and the koala has its thumb 

 and index fingers capable of being opposed to the 

 others. 



Some fossil kangaroos, like the Diprotodon, were of 

 great size ; one thigh bone of this animal in the museum 

 of the University of Dublin, must have been at least 

 two feet in length when complete. It is also interesting 

 that the earliest fossil mammals which have as yet been 

 discovered are marsupials. The bones of marsupials 

 are, in general, easily recognised ; thus the lower jaw 

 has an inflexed angle, whereby it can be distinguished 

 from that of any other mammal. The dentitions of 

 marsupials are very variable, as can be seen from the 

 four subjoined examples : 



Kangaroo (fig. 37) 



* /i^4 4 



i i 



Myrmecobius or) 7 4~ 4 r I ~ I p 2 ~ 2 *f55 

 banded anteater) 33' i i' 33' 66' 



Tasmanian devil) r 4 4 r i i P 2 2 ,,-4 4 

 (fig. 35) J3^3 i=?^J=?. ' 4=? 



