152 



MAMMALS 



Figure 164. — Brown Bat. 

 Showing formation of wings. 



getting in the squirrel, for burrowing and locomotion in 

 the moles, for flying in the bats, and for swimming in the 



seals. In all fore limbs 

 of mammals, even in 

 those as different as the 

 leg of the squirrel, the 

 flipper of the seal, and 

 the wing of the bat, the 

 arrangement of the 

 bones is the same. The 

 hind legs of mammals do 

 not show so much varia- 

 tion as the fore limbs. 

 But in some cases, as in 

 the whale, the hind legs 

 have practically disap- 

 peared through disuse, 

 and there is no external 

 evidence of them. Some 

 animals, like the bears, 

 walk on the soles of their 

 Figure 165. — Flying Squirrel. feet, and some, like the 



