CHAPTER XVII 

 THE HUMAN BODY AND ITS FOOD 



350. Chief Divisions of the Body. The science that 

 deals with the organs of plants and animals, and with the 

 functions of these organs, is called Physiology. The 

 science of the human body is called Human Physiology. 

 In Chapter XVI we learned that while in animals below 

 fishes (invertebrates) the parts supporting the body, if 

 there are any, are on the outside of the body, in fishes and 

 the animals above them (vertebrates) the framework of 

 the body is on the inside, and takes the form of a bony 

 skeleton. Along with this change in the body framework 

 there is also a change in the position of the nervous sys- 

 tem; in the vertebrates the important nerve centers are 

 all on the dorsal side (the back). We therefore think of 

 the body of a fish as having two spaces, or cavities: (1) a 

 dorsal cavity, consisting of the brain space (skull) and 

 the long narrow space (canal) inside the spinal column; 

 and (2) a ventral cavity. The ventral cavity is much the 

 larger, and contains the organs of respiration, circulation, 

 digestion, etc. 



In mammals we make the same body divisions as in the 

 fish, but we divide the ventral cavity into two distinct 

 parts: (1) the thorax, and (2) the abdomen. 



The diaphragm forms the dividing wall between these 

 two parts. In man (Fig. 273) these same divisions exist. 

 The thorax contains the lungs, the heart, some large 



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