352 



VERTEBRATE ANIMALS. 



The Cheiroptera or Bats are essentially characterised by the fact that 

 the fore -limbs are much longer than the hind -limbs, and have 

 several of the fingers enormously elongated (fig. 2.56). These enor- 

 mously lengthened digits are united by an expanded leathery mem- 

 brane or "patagium," which not only stretches between the fingers, 

 but is also extended between the fore and hind limbs, and is 

 attached to the sides of the Ijudy (fig. 2.57). The patagium thus 

 formed often includes the tail, and is nearly or quite naked or 

 destitute of hairs on both sides. It is used as an organ of true 

 flight, and, in accordance with this, there are well-developed collar- 

 bones (clavicles), and the breast-bone is furnished with a ridge for 

 the attachment of the pectoral muscles. Of the fingers of the hand 



Fig. 257. — Cheiroptera. VespertiUo discolor, one-half the natural size. 



at least three are destitute of nails. The mammary glands are 

 placed upon the chest. Teeth of three kinds are always present, 

 and the canines are always well developed. 



The Bats are all twilight-loving or nocturnal animals, and they 

 are the onh' Mammals which jjossess the power of true flight, though 

 several others can make extended leaps from tree to tree. The eyes 

 are small, but the ears are very large, and their sense of touch is 

 most acute. During the day they retire to caves or ci'evices in 

 rocks, where they suspend themselves by the liind-feet, which are 

 provided with curved claws. In their flight, though they can turn 

 with great ease, they are by no means as rapid and active as the 



