76 MAMMALIA. 



their organization^ which produce analogous differences in 

 their habits, and to such an extent as makes it impossible to 

 arrange their genera on one line, and compels us to form them 

 into several families, which are variously connected by multi- 

 plied relations. 



FAMILY I. 



CHEIROPTERA. 



This family still retains some affinity with the Quadrumana 

 by the pendulous penis, and by the mammae which are placed 

 on the breast. Their distinguishing character consists in a 

 fold of the skin, which, commencing at the sides of the neck, 

 extends between their four feet and toes, supports them in the 

 air, and even enables such of them to fly as have their hands 

 sufficiently developed for that purpose. This disposition re- 

 quired strong clavicles and large scapulse to give the necessary 

 solidity to the shoulder, but it was incompatible with the ro- 

 tation of the fore-arm, which would have diminished the force 

 of the stroke requisite for flight. They have all four great 

 canini, but the number of their incisors varies. They have 

 long been divided into two genera, founded upon the ex- 

 tent of their organs of flight. The first of these, however, 

 requires several subdivisions. 



Vespertilio, Lin. 



The arms, fore-arms and fingers of the Bats are excessively length- 

 ened, forming, with the membrane that occupies their intervals, 

 true wings, possessing even a greater extent of surface than those 

 of Birds they consequently fly very high, and with great rapidity. 

 The thickness of their pectoral muscles is proportioned to the mo- 

 tions they have to execute, and there is a ridge in the middle of the 

 sternum like that of Birds, to which they are attached. The thumb 

 is short and armed with a claw, by which they are enabled to creep 

 and to suspend themselves. Their hind feet are weak and are divided 

 into five toes, almost always of equal length, armed with trenchant 

 and pointed nails. They have no caecum. Their eyes are exces- 

 sively small, but their ears are frequently very large, and together 

 with the wings form a vast membranous surface, which is almost 



