INTEODUCTION. 



The Animal Kingdom was divided by Cuvier into four great divi- 

 sions or sub-kingdoms — Vertebrata, Mollusca, Artieulata and Radi- 

 ata. The last of these has been greatly divided of late, and the 

 limits of two of the others been slightly altered. 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, I'ishes 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-appli- 

 cability to the CetacesB, has properly been allowed to become obsolete. 



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



