CHARACTERISTICS OF MAMMALS 3 



become adult, but the rat family and most remaining gnawers 

 have no milk teeth. 



The incisors, or cutting-teeth, may number three, two, or 

 one on each side; some marsupials even have four upper in- 

 cisors. They may be chisel-like or ever-growing, as in rodents 



Incisors 



Fig. I— Mammalian teeth, exemplified hij the teeth of the 

 Marsupial Cat 



and rabbits; pincer-like, as in some insect-eaters; broad and 

 spade-like, as in cattle and some monkeys ; or small and almost 

 useless, as in some bats. They are often about equal in size 

 and shape, as in meat-eaters and monkeys; or the middle m- 

 cisor may be much larger than the other, as in the rabbit, or 

 lost completely, as in the upper jaw of some bats. Upper in- 



