MAMMALIA. 553 
throughout of a double fold of skin. There is no external 
tail. In the Microchiroptera the tail is well developed and 
forms an axial support for the interfemoral membrane. 
By this means the latter group are able to turn rapidly in 
the air in pursuit of insects, 
The sense of touch is remarkably developed in bats, 
some families having a pair of peculiar organs, the “nose 
leaf,” on the snout. It consists of an irregular cutaneous 
expansion, supplied by the fifth nerve, and apparently 
enables the animal to be cognisant of variations in vibra- 
tions of the air caused by objects in close proximity. In 
a great number of bats the ear-pinna is also enormously 
developed, though not excessively so in our type. 
The bat has lost almost all power of terrestrial locomo- 
tion and at best can shuffle clumsily along the ground. 
This is due to the great reduction of the hind-limbs and 
especially to the fact that the knees, in connection with the 
support of the patagium, are bent backwards like the elbows, 
making them unfit for walking. The “wings” are also 
quite unsuited for the same purpose. The hind-limbs are 
used for grasping boughs, and the bat thus hangs suspended 
head downwards, often enveloped in its patagia. We have 
already noticed that the zrial types have been evolved from 
the arboreal, and in this respect the MMegachiroptera are 
less specialised than the Aficrochiroptera, as their food and 
resting-place are arboreal. 
The bats were for a long time regarded as birds, or at 
least not recognised as true mammals. There is, however, 
if possible, less difficulty in noting their mammalian affinities 
than in the case of the porpoise. A reference to the two 
columns of Aves and Mammalia in Table, page 431, will 
make this quite clear. The generally accepted view regards 
them as modified Jnsectivora. 
The skull is very variable in general form and structure 
throughout the group. The fox-bat has a fairly even set 
of teeth, well defined into incisors, canines and molars, the 
canines being slightly the longest. There are only two 
incisors in each jaw, a common condition in bats, though 
the lower jaw may have as many as three. The molars 
and premolars have blunt crowns and are 3. No bats 
have more than $ or 33. 
