COMPARATIVE DENTAL 

 ANATOMY 



CHAPTEE I 



GENERAL ZOOLOGY AND COMPARATIVE 

 ANATOMY 



The Animal Kingdom is divided into two sub- 

 kingdoms, — viz., (a) Invertebrates and (b) Verte- 

 brates. These sub-kingdoms are further sub- 

 divided into classes; classes are divided into or- 

 ders; orders into families; families into genera; 

 and genera into species. Species is the last divi- 

 sion into which animals can be classified, but if 

 the individuals of a species vary much from the 

 normal type, they may be classed as sub-species 

 or varieties. All animals are grouped with refer- 

 ence to their plan of structure, and classification 

 is made according to the system of organization, 

 and without regard to superficial characters or 

 resemblances except so far as external features 

 may have reference to functions. 



Vertebrates and Invertebrates are distin- 

 guished from each other by the presence or ab- 

 sence of a vertebral column or backbone. The 



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