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 aerial types have been evolved from 

 the arboreal, and in this respect the Alegachiroptera are 

 less specialised than the Microchiroptera^ 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 difificulty 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 Insectivora. 



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 a nd are |-. No bats 

 hav€ more than ^ or f;f. 



