BATS OK HAND-WINGED ANIMALS 255 



their way through the air. So we find that it also is furnished with 

 organs of flight, and those of so useful a character that the animal is 

 really able to fiy as well as many birds. 



A peculiarity in the bat's structure is that the fore limbs take the 

 form of wings, and are connected with the body by means of a delicate 

 skin-like membrane. This membrane, indeed, is nothing more than 

 the skin of the fianks, which is greatly widened, and is stretched 

 between the bones of the hand, running along the body as far as the 

 tail. Like the body itself, it has its upper and lower surfaces, which, 

 with a little care, may be separated from one another, even though in 

 some parts of the wing the membrane is so extremely thin that, with 

 the aid of a good microscope, the blood may be clearly seen as it courses 

 rapidly through the threadlike vessels which run to all parts of the 

 organ. 



Now, this membrane, to be of service, must, of course, be 

 stretched upon a framework, and this framework is supplied by the 

 bones of the hand and arm. The entire wing, indeed, is very much 

 like a boy's kite, if we imagine the shape to be a little altered, for 

 the wooden cross pieces are represented by the bones of the arm and 

 fingers, and the linen or paper which is stretchd across, by the skin- 

 like membrane. 



If you were to take a dead bat and to carefully strip the skin 

 from the wing you would find that the bones are most curiously altered 

 in form, being not only extremely light and slender, but also of really 

 wonderful length. The middle finger alone, for instance, is fully as 

 long as the entire body. 



Nature has taken away the second bone of the lower arm of the 

 bat, or, to speak more strictly, has left it in a small and imperfect form, 

 so that the limb cannot revolve from side to side. The stroke of the 

 wing, therefore, is firm and regular, and flight is rendered quite easy 

 so that the bat can remain for hours in the air without feeling the 

 least signs of fatigue. 



The fingers, again, which are not intended to be used for grasp- 

 ing purposes, are perfectly rigid, and cannot be bent downwards 

 toward the palm of the hand. Tlieir only motion, indeed, is a side 

 one, so that the wrings, when not in use, can be closed just like a lady's 

 fan, and folded neatly away by the sides of the body. 



