Bat v 3 1 



Though possessing an almost equal power of flight 

 with the birds, the wings of the bat are by no means 

 constructed upon the same principle. Instead of 

 feathers, the wing is composed merely of a membrane 

 tightly stretched between the bones of the fingers, 

 and extending along the sides as far as the tail. In 

 order to fully understand this structure, we must 

 examine the modifications of the skeleton whicli 

 render it possible. 



In the first place, the framework of the wing of 

 the bat is formed merely by the bones of the arm and 

 hand, which, more especially those farthest from the 

 body, are elongated to a wonderful extent, the middle 

 finger being actually of greater length than the whole 

 head and body of the animal. The only exception 

 is the thumb, which is very short, and armed with a 

 strong curved claw. 



Not only are the bones of the fingers elongated, 

 but those of the palm of the hand, or ' metacarpals,' 

 are drawn out to an astonishing length, that of the 

 thumb being excepted, as above mentioned. 



If we spread our own fingers widely, we shall see 

 that their bases are connected by a fold of skin which 

 is hardly perceptible when the hand is closed. Now 

 and then, it is extended as far as the first joint, and 

 there are many of the mammalia in which it is still 

 further developed. The seals which fly through the 

 water have the hand membrane greatly extended, 

 and other water-living mammalia have it developed 

 in a lesser degree. 



Then, the flattened skin-fold of the flanks is not 

 peculiar to the bat tribe. It can be traced in the 

 common squirrel, and in the flying lemurs, flying 

 squirrels, and flying opossums a similar structure is 

 seen. 



In the lower part of the arm, that from the elbow 



