INTRODUCTION. 



the hands and arms, as an apparatus of flight, supposes great power in 

 the muscles by which they are governed : hence the length and strength 

 of the clavicles, and the size of the scapulae, and of the keel, which, as in 

 birds, runs down the sternum, for the attachment of voluminous muscles, 

 destined to work the expansive organs of flight. It is a curious circum- 

 stance, that the membranous wings of these animals (and the expanded 

 membranous ears of many of them), are the scat of a most refined degree 



Skeleton of a Bat. a, scapula; b, clavicle; c, sternum, with its elevated keel; rf,humerus; #, radius; /,ulna; g-, carpus; 

 A, metacarpal bones ; t, phalanges of fingers ; k, the thumb. 



of sensibility : they are supplied abundantly with nerves ; and, as experi- 

 ments prove, are capable of appreciating the vibrations of the atmosphere, 

 its currents, and its quiescence, to such a nicety, that, if the eyes of a 

 Bat be covered, it directs its course, avoiding obstacles in its way, and 

 threading the intricacies of obstructed passages, apparently with as much 

 facility as though its sight were in perfect exercise. 



The spade-like hand of the Mole (figs. 82, 83, 84,) affords another 



example of the modifications of this organ for an especial purpose. Its 

 anterior extremities are admirably adapted for the mining operations in 

 which it employs its existence. The first thing that strikes us is the 



