CHARACTERISTICS OF MAMMALS 7 



and weasel families among the meat-eaters, walk on their flat 

 feet and hands. 



Monkeys and their allies usually walk on their palms and 

 soles, and most have nails rather than claws. The lemurs and 

 tarsiers have claws on some toes and nails on others. The gib- 

 bons and orang-utan swing from branch to branch suspended by 

 their long arms ; they seldom come to the ground. 



Bats have hook-like claws on their hind feet and thumbs. 

 The rest of the fore limb is greatly modified. The bones of the 

 arm and hand are lengthened; the third finger alone may be 

 longer than the bat's body, and the forearm (the part between 

 wrist and elbow) is almost as long. This bony framework is 

 covered with nearly naked, elastic skin extending between the 

 hand and ankle, and frequently also between the legs and tail. 

 The skin between the hind legs and tail is called the interfemoral 

 membrane. It is used as a brake and rudder. The hind limbs 

 are so constructed that the knee bends backward. 



CLASSIFICATION AND SCIENTIFIC NAMES 



It is a part of human nature to group things in orderly ar- 

 rangements and to abstract general ideas. The animal world 

 is so complex that unless it is arranged and thought about sys- 

 tematically, it cannot be well understood. Men have been classi- 

 fying mammals in various ways for thousands of years. They 

 divided them into those that were good or bad to eat, or those 

 that were harmless or dangerous. In the Bible a different clas- 

 sification was made: animals with divided hoofs which chewed 

 the cud were considered fit to eat ; the rest were "unclean." 

 Modern classification is based instead on fundamental similarity 

 of structure and what we know about the evolution and descent 

 of animals from common ancestors. 



Since man is a mammal, he may be chosen to illustrate differ- 

 ent stages in a simplified classification. The Class Mammalia 

 is divided into two Subclasses ; man is placed in the Subclass 



