INTRODUCTION. 89 



Division of the Class Mammalia into Orders. 



Naturalists have distributed the whole animal 

 creation into classes and orders, and, without even 

 excepting man, into families, according to affinities 

 they bear with others more or less consirnilar : the 

 further divisions are into genera, and these into spe- 

 cies and varieties ; but it has been found convenient 

 to sub-divide occasionally the classes into sub-classes, 

 the families into sub -families or tribes, genera into 

 sub-genera or groups, and in these there have been 

 recognised forms, where, apparently, one typical 

 species is surrounded by others so nearly alike, that 

 the question of variety, or of difference, cannot be 

 completely decided. 



The characters of mammalia, by which Cuvier 

 chiefly distinguished one from another, are derived 

 from the organs of touch, which indicate their de- 

 gree of dexterity, and from the organs of mastica- 

 tion, which determine the nature of their food, and 

 necessarily point out the form and functions of the 

 organs connected with digestion, and a variety of 

 other circumstances, even such as relate to their in- 

 telligence. The perfection of the organs of touch is 

 estimated by the number and mobility of the digits, 

 according as they may be more or less inclosed in 

 claws or hoofs. A digit, which has a great part of 

 the extremity sunk into a hoof, is denied the exer- 

 cise of feeling and of prehension ; the opposite ex- 

 treme shows a nail, composed of a single lamina, 



