ORDER CHEIROPTERA ; GENERAL CHARACTERS. 183 



number of which varies in different genera ; being only one in 

 the first finger, but four in the second, in the specimen here 

 figured. These taper to a point, and are not terminated by 

 claws or nails. The thumb, however, does not partake of this 

 extension in length, nor does it assist in the support of the wing- 

 membrane ; but it is short and free, and is terminated by a 

 hooked claw. The clavicle, c/, and scapula, o, to which are 

 attached the muscles that move this member, are of great 

 strength ; and the sternum, or breast-bone, has a keel-like projec- 

 tion, similar to that which exists in Birds (ANIM. PHYSIOL. 

 89) for the attachment of the powerful muscles by which the 

 wing is drawn down. The hinder limbs do not present any- 

 thing peculiar in their structure ; they serve to assist in keeping 

 the wing-membrane extended (as does also the tail, where it 

 exists) ; and the toes are five, armed with sharp claws, by which 

 the animal can suspend itself, when at rest in its retreat. 



166. The whole powers of the animal seem concentrated 

 upon its organs of flight ; and when it is neither asleep nor 

 torpid, this kind of movement is evidently its natural condition. 

 It can only move along a solid surface, by folding its wings, and 



using the hooked thumbs to lay 

 hold of any inequality, and to 

 draw itself forwards. Hence 

 its motions are awkward and 

 shuffling ; and on a polished 

 surface, like that of a table, it 

 is greatly embarrassed. But 

 in the hollows of trees, the 

 crevices of ma snr and the 



F, G .86.-BAT 



chinks or fissures of a rock, it 



can climb and crawl about with great facility. The air, how- 

 ever, is its home ; and through this it moves with vast rapidity, 

 and with great apparent ease, wheeling in every direction in 

 search of its insect prey, and performing the most abrupt evolu- 

 tions to secure it. In these movements it is very much assisted 

 by the tail, which serves as a rudder ; and we shall find that 

 this organ is most developed in the Bats which pursue insects on 



