14 INTRODUCTION. 



ology of the Horse ; and its Morphology, the special study 

 of the form of the adult animal and of its internal organs. 



Thus far we have been looking, as it were, at a steam- 

 engine, with the fires out, and nothing in the boiler ; but the 

 body of the living Horse is a beautifully formed, active ma- 

 chine, and every part has its different work to do in the 

 working of that machine, which is what we call its life. 

 The science of such operations as the grinding of the food 

 in the complex mill of the mouth ; its digestion in the labo- 

 ratory of the stomach ; the pumping of the blood through a 

 vast system of pipes over the whole ]?ody ; its purification 

 in the lungs ; the process of growth, waste, and repair ; and 

 that wondrous telegraph, the brain, receiving impressions, 

 sending messages to the muscles, by which the animal is en- 

 dowed with voluntary locomotion this is Physiology. ' But 

 Horses are not the only living creatures in the world ; and 

 if we compare the structures of various animals, as the Horse, 

 Zebra, Dog, Monkey, Eagle, and Codfish, we shall find more 

 or less resemblances and differences, enough to enable us to 

 classify them, and give to each a description which will dis- 

 tinguish it from all others. This is the work of Systematic 

 Zoology. Moreover, the Horses now living are not the only 

 kinds that have ever lived ; for the examination of the 

 earth's crust the great burial-ground of past ages reveals 

 the bones of numerous horse-like animals : the study of this 

 pre-adamite race belongs to Paleontology. The chronologi- 

 cal and geographical distribution of species is the depart- 

 ment of Distributive Zoology. Speculations about the ori- 

 gin of the modern Horse, whether by special creation, or by 

 development from some allied form now extinct, are kept 

 aloof from demonstrative science, under the head of Theo- 

 retical Zoology. 



2. History. The Greek philosopher Aristotle (B.C. 384- 

 322) is called the " Father of Zoology." Certainly, he is the 

 only great representative in ancient times, though his fre- 

 quent allusions to familiar works on anatomy show that 

 something had been done before him. His " History of 

 Animals," in nine books, displays a wonderful knowledge of 

 external and internal structure, habits, instincts, and uses. 

 His descriptions are incomplete, but generally exact, so far 



