30 ANIMAL LIFE OF THE BRITISH ISLES. 



BatS (Chiropterd). 



With the exception of the great class of Birds, the Bats are 

 the only surviving back-boned animals that possess the organs 

 of true flight. Apart from this specialisation for a life in the air 

 the Bats are very similar in their organisation to the Insectivora, 

 and long ago Huxley pointed out that they were exceedingly 

 modified Insectivora ; but this modification marks them off 

 sharply from their nearest allies, and the authorities have 

 agreed that it constitutes a reason for setting them apart in a 

 special order the Chiroptera or wing-handed animals. 



So complete has been the adaptation to an aerial life, in- 

 volving both pairs of limbs, that they are no longer fitted for 

 progression on the earth. The fingers of the hand have been 

 so drawn out that they are longer than the forearm, and the 

 middle finger is at least equal in length to the head and body, 

 whilst the thumb has been converted into a hook by means of 

 which the Bat can hang from any rough surface. Over these 

 exaggerated finger-bones abroad web of skin has been stretched, 

 and connected not only to the sides of the body but also to the 

 hind legs as far as the ankle, and then nearly or quite to the 

 tip of the slender tail. The effect of this great modification, 

 whilst it creates a pair of great wings, is to render the hind 

 limbs unfitted for ordinary locomotion, for these are so twisted 

 out of the position assumed in quadrupeds that the knees are 

 turned backwards. This is the cause of the awkward, shuffling 

 movements of a Bat on the ground which make it quickly 

 rise into the air or at least to climb some vertical surface. 



Looking at the skeleton of a Bat, we shall find the vertebral 

 column short, the neck short-boned but broad, the spinal cord 

 being of great thickness at this part though reduced to "a mere 

 thread at the hips. The ribs are usually flattened and con- 

 nected to a strong breast-bone, which has a prominent keel for 

 the attachment of powerful muscles controlling the wings. The 



