32 Anecdotal Natural History. 



to the wrist, there is practically one bone only, instead 

 of two, as is usually the case, the reason of which is 

 very apparent. It is owing to the two bones of the 

 arm that we are enabled to turn the limb inwards and 

 outwards at the elbow. If the bat were possessed of 

 the same power, it would be impossible for the wing 

 to strike the air with the steady beat necessary to 

 flight, for the resistance of the air, turning, the arm 

 sideways, would allow the wing to cleave through it 

 sideways, and the power of the stroke would thus be 

 of no avail. As it is, however, being one bone only, 

 the bat is unable to turn the limb, which therefore 

 always presents its full surface to the air. 



The bones of the hand, too, cannot be clenched as 

 in a fist, but possess a side motion only, enabling 

 the wing, when not in use, to be folded closely against 

 the body. 



The membrane which forms the wing is merely a 

 prolongation of the skin of the flanks and other 

 parts of the body, stretched tightly between the 

 finger-bones, and extending as far as or farther than the 

 tail, which, in the insect-eating species, is included in 

 it, serving, like the tails of birds, as a natural rudder 

 by which the animal can direct its course. In the 

 fruit-eating bats, however, where so great agility in 

 the air is not necessary, the tail is left partly or 

 entirely free, and is much used in climbing and 

 walking. 



The membrane is a double one, very thick in those 

 parts contiguous to the body, but so delicate near the 

 edges, that by the aid of a microscope the blood 

 corpuscles can be seen passing along the vessels that 

 supply the wing. 



Though the powers of flight of the British bat are 

 fully equal to those of many birds, they have never been 

 known to migrate from one country to another, and 



