88 CLASS MAMMALIA. 



flanks. The back and the belly furnish each a leaf as we 

 may be assured of by separating the membrane of the 

 wings. Notwithstanding, however, that this membrane is 

 formed of two skins, pasted as it were together, it appears 

 to us but a sort of slender, light, and transparent net- work. 

 Thus, as the bones of the hand are only elongated by dimi- 

 nishing in thickness, in like manner the tegumentary system 

 is not extended but by growing slender in a similar propor- 

 tion. Here it is worthy of remark, that a general law of all 

 organization is made to contribute in a wonderful manner 

 to facilitate the aerial movements of the cheiroptera, for 

 bones more compact, and a membrane of greater density, 

 especially at such a distance from the vis motrix, would 

 have added a momentum to the bodies of these animals, 

 that all their efforts to surmount would not have overcome. 



This analysis of the wing of a bat, by presenting to us the 

 arm and hand of a mammiferous animal, the metacarpi and 

 phalanges of which are united by membranes, is not only 

 sufficient to convince us that there is no analogy between it 

 and that of a bird, but must also lead to the consideration 

 of such extremities in the mammalia as are the best calcu- 

 lated for seizing objects, and the most profoundly divided. 

 This will be necessary before we can perfectly understand all 

 the anomalies of this singular organ. Now we find that the 

 mammalia which possess the deepest digitations are the 

 quadrumana; and as we find that in this particular the bats 

 are next, we are led to conclude that Linnaeus judged cor- 

 rectly of their natural affinities. But we are still more com- 

 pletely led to this conclusion by considering other traits of 

 their conformation. 



The farther we remove from the quadrumanous groups, 

 who have the mammillary glands situated on the thorax, the 

 more we observe those glands descend from the breast to 

 the abdomen. All the bats, with the exception of one sub- 

 division (the Rhinolphi) have teats exactly resembling those 



