MAMMALS 



479 



glands. There is a special arrangement obviating the danger 

 of choking, for the top of the wind-pipe is drawn out into a 

 sort of cone fitting into the back of the nasal passages, but 

 leaving room on either side of it for milk to pass down into the 

 gullet. Even after the young animal is able to run about, it 

 continues for some time to use the pouch as a retreat (fig. 997). 



Fig. 997. Yellow-footed Rock- Wallaby (Petrogale xanthopus], with young one in her pouch 



The young of climbing Marsupials are in a number of cases 

 carried on their mother's back, after they have grown sufficiently 

 large and strong to hold on with safety (fig. 998). This is the 

 case, for example, in the Koala (Phascolarctos) of Australia, 

 and the little Mouse Opossum (Didelphys murina) of South 

 America. The numerous offspring of the latter twine their pre- 

 hensile tails round that of their mother, which greatly conduces 



