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 mamme 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 
airy and even enables such of them to fly as have their hands 
sufficiently developed for that purpose. ‘This disposition re- 
quired strong elavicles and large scapule 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. — mary have 
long been divided into two genera, founded upon | the ex- 
tent of their organs of flight. The first. of these, however, 
requires Sorerag baayasions. 
’ i> Aa 5 
- * VESPER TILIO, Lin. yi 
The arms, fore-arms and fingers of the Bats are Picessimely 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 isa 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 mo cecum. Their eyes are exc 
sively small, but their ears are frequently very large, and ‘ogetl 
with the wings form a vast membranous surface, which is almost | 
