ELEMENTS 



OF 



MAMMALIAN ANATOMY 



INTRODUCTION 



Since this book is designed for the use not only of students 

 who have pursued the study of biology for some time, but also 

 for those making their first actual acquaintance with the sub- 

 ject, it may be well to call attention to the fact that any animal 

 or plant may be considered from several different standpoints. 

 A general study of structure and of the relations of the various 

 systems and organs is known as Anatomy. Histology concerns 

 itself with the cell and cell aggregates or tissues composing the 

 organs. These two sciences are included in Morphology, a term 

 which by many is made to include also Embryology or Ontogeny, 

 treating of the development of an organism from the egg, or its 

 vegetable homologue, to the period of assuming adult charac- 

 teristics. Since ontogeny deals not only with the growth of 

 structure but also the process of growth, it may likewise be in- 

 cluded under Physiology, a science which has for its province 

 the investigation of the functions of the organs and systems. 

 A special field of physiology having for its consideration the 

 operations, especially the conscious operations of the nervous 

 system, constitutes the science of Psychology. 



The same species of animals are not found in all parts of the 

 world. The lion and tiger are found wild only in the old world, 

 while the opossum is confined to the new world. Again, many 

 species of animals whose fossil remains indicate their existence 

 on earth several millions of years ago, have at present no living 



