248 
BATS. 
cannot be extended in an upward direction beyond the limits of the impetus of the 
original leap. 
This power of true flight is, then, the essential characteristic of all bats; and 
it is a very remarkable fact that among all the host of extinct animals with which 
we are now acquainted, none have been discovered in any way connecting bats with 
other Mammals. Indeed, remains of bats very closely resembling existing kinds 
are met with in the upper part of the Eocene period, which show that the order 
is a very ancient one, and that we should have to go back still earlier before 
creatures intermediate between bats and other Mammals were met with. In spite 
of this, naturalists have, however, no hesitation in believing that bats have taken 
origin from Mammals of ordinary terrestrial habits. It is found, indeed, that in 
their essential structure bats are so closely allied to the Insectivores (of which 
we treat next), such as shrews, moles, etc., that there can be little doubt of their 
derivation from the ancestral forms of that order; and it is probable that the 
power of true flight was developed gradually from spurious flight, like that of 
flying squirrels. Moreover, it will be shown later on that there is a very curious 
kind of Insectivore, endued with the power of spurious flight, which may give us 
some inkling; of the manner in which bats have been derived from the earlier 
members of that order of Mammals. Bats are accordingly regarded by zoologists 
as neither more nor less than Insectivores, specially modified and adapted for an 
aerial life. Moreover, as there appear to be indications that the Insectivores were 
connected with some of the extinct lemurs, it is now considered best to place them 
and the bats immediately after the Primates. This must not, however, be taken 
as any indication that these groups really occupy a high position in the zoological 
scale; the fact really being that their organisation is of a low type, and far 
inferior to that of the Carnivores which are placed later on. 
The most obvious and important characteristic of bats being 
’ their faculty of flight, and the apparatus for this being mainly 
furnished by the fore-limb, the order to which they belong has been appropriately 
named Chiroptera, or hand-winged. In the great majority of Mammals the hind- 
limbs are as large as, or larger than, the front pair, but in bats the latter (as is 
well shown in the figure of the skeleton at the head of this chapter) vastly 
exceed the former in length. In a bat’s wing the humerus of the upper 
arm is only moderately elongated, but the single complete bone in the fore¬ 
arm, corresponding to the human radius, has a far greater length, and this ex¬ 
traordinary elongation is carried to a still greater extent in the bones of the 
hand, all of which, with the exception of those of the thumb, form long slender 
rods. The thumb is free, and terminates in a hooked claw, which can be used for 
the purposes of climbing or suspension; but the fingers, of which the third is the 
longest, are connected together by the delicate membrane constituting the soft part 
of the wing. This wing-membrane is continued along the arm and the sides of the 
body, and thence to the hind-legs. There is, moreover, a similar membrane 
connecting the two hind-limbs with the generally long tail; this membrane being 
usually supported by a peculiar spur of bone projecting from the foot. The toes 
are, however, quite free. In consequence of the connection of the hind-limb with 
the wing-membrane, the knee-joint is directed backwards instead of forwards in 
