2 HUMAN PHYSIOLOGY 



most part must be directed to ascertaining first, 

 man's place in nature ; second, the particular build 

 of the frame he owns. 



MAN'S PLACE IN NATURE. Man stands at the 

 head of the animal kingdom, and as such becomes 

 in turn the chief figure in the class of animals 

 popularly known as " quadrupeds " and scientifically 

 as "mammalia." In turn, this class forms one of 

 the five divisions of the type of animals known as 

 Vertebrates, or " back-boned " forms. In all of these 

 animals the presence of a back bone or spine forms 

 a distinctive feature, for even in the very lowest, 

 represented by certain fishes, if a bony spine itself 

 is not developed, we find in such animals a struc- 

 ture representative of the back bone itself. Man's 

 superiority over all other members of his class, and 

 therefore over all Vertebrates, is represented by 

 features which really represent elaborations or 

 evolutions of the structures found in his lower 

 neighbours. For example, the bodies of all the 

 back-boned animals are built on one and the same 

 type. If we make a section, in the long direction of 

 the body of a fish, for example we find that the 

 skull and spine protecting the main centres of the 

 nervous system brain and spinal cord occupy 

 the back or dorsal region of the body. In the middle 

 we find the digestive system, which is essentially a 

 tube ; whilst situated lowest we find the heart. 

 Between the digestive system and the back bone 

 there exists a second nervous system known as the 

 sympathetic system, a structure typically repre- 

 sented by a double chain of nerve-knots or centres 

 with connecting nerves. Now this plan runs entire 

 and unbroken through the whole Vertebrate series 

 of animals, from fish to man. 



