INTRODUCTION. 



THE Animal Kingdom was divided by Cuvier into four great divisions 

 or sub- kingdoms Vertebrata, Mollusca, Articulata, and Radiata. 

 The last of these has been greatly divided of late, and the limits of two 

 of the others have been slightly altered. The Vertebrata are essentially 

 distinguished from the others by the possession of an internal osseous 

 frame or skeleton, enclosing a distinct brain and spinal cord. They 

 never have more than four limbs ; the mouth consists of two jaws 

 placed vertically, the blood is red, and they have distinct organs of 

 vision, hearing, taste, and smell. 



Vertebrate animals comprise four distinct classes, some of which 

 are cold-blooded, i.e., with blood nearly the temperature of the 

 surrounding medium, Fishes and Reptiles ; whilst the others are 

 warm-blooded, Birds and Mammals. The former have been already 

 treated of in this series. 



Mammals are warm-blooded, viviparous animals, and are distin- 

 guished from Birds, as well as from the other vertebrated animals, 

 by the possession of mammary glands, secreting a nutritious fluid 

 called milk, for the nourishment of their young, and terminating 

 outwardly in all (except one or two) by teats. They are also distin- 

 guished by a covering of hair, entire or partial. Whales appear to be 

 exceptional ; but even in these the foetus has some tufts of hair. 



The lungs are free, and are separated from the abdominal viscera by 

 a muscular partition called the Diaphragm, which is also one of the 

 chief agents for inspiration. Most animals have four limbs ; hence the 

 old term Quadruped, which, on account of its non-applicability to the 

 Cetacea, has properly been allowed to become obsolete. 



Mammals, says Cuvier, require to be placed first, because they 



