550 THE MECHANICAL FUNCTIONS. 



enabling the animal to flutter in the air, and 

 to break its fall during its descent from the 



222 



branches of trees. Structures of this kind are 

 possessed by the Sciurus volans, or flying squir- 

 rel, and also by some other species of the same 

 genus. They are seen on a still larger scale in the 

 Lemur volans, or Galeopithecus. The resistance 

 which these broad expansions of skin oppose to 

 the air, when the limbs are spread out, enables 

 the animal to descend in perfect safety through 

 that medium from very considerable heights : 

 but these appendages to the body are mere para- 

 chutes, not wings, and none of the animals which 



