With the exception of the great class of Birds, the Bats are the only surviving backboned 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, involving 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 a broad 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 connected to a strong breastbone, which has a prominent keel for the attachment of powerful muscles controlling the wings. The tail controls the web connecting the hind legs, which acts as a rudder in flight and as a net helping to capture and retain the larger insects upon which the Bat lives. [Illustration: _Pl. 12._ _C 30._ *Lesser or Pigmy Shrew.* Sorex minutus.] [Illustration: _Pl. 13._ _C 31._ *Great Bat or Noctule.* Nyctalus noctula.] The permanent teeth--which are quite different from the milk-teeth--vary in the different species, but they always have distinct roots, and in the British species the upper surface always runs into points or cusps, suited for cracking the chitinous shells of beetles.