VERTEBRATA. 271 



bara, Beaver, and Porcupine. The order also contains 

 Squirrels, Rats, Mice, and Agoutis. The Beaver has a 

 smooth, unconvoluted brain, yet shows great ingenuity 

 in constructing its dwelling, felling logs with its teeth, 

 building them into a dam, and arranging others as a 

 shelter, plastering them with mud made into mortar by 

 its flat, trowel-like tail. The Flying-squirrel (Pteromys) 

 possesses a cloak of skin, stretching between the fore and 

 hind limbs, enabling it to sustain short flights in the air. 



Order 5. Insectivora, (insect-eating.) These are di- 

 minutive animals, as the Shrew, the Hedgehog, and the 

 Mole. They have incisor, canine, and molar teeth, and 

 the latter have numerous pointed cusps. They have a 

 long muzzle, short legs, and clavicles. The feet are 

 formed for walking or grasping, and are plantigrade, 

 five-toed, and clawed. The Hedgehogs have a spiny 

 exoskeleton, covering the entire body, and lined by a 

 broad muscle, which, when it contracts, rolls the animal 

 into a ball. 



Order 6. Cheiroptera, (cheir, a hand ; pteron, a wing,) 

 are distinguished by long fore-limbs, adapted for flight, 

 the fingers being very long, and united by a membra- 

 neous web. The toes and one or two of the fingers are 

 armed with hooked nails. The Bat may be called the 

 only true flying Mammal, since it is capable of rapid 

 and long-continued flights. (Fig. 166.) The Vampire- 

 bat has a curious leaf-like expansion of the skin cover- 

 ing the nose. The ears of Bats are very large, and 

 copiously supplied with nerves of touch. The sense of 

 hearing is also acute. 



Order 7. Cetacea, (Ketos, a whale,) are fish-like in form 



