HUMAN BIOLOGY 



CHAPTER I 

 THE GENERAL STRUCTURE OF THE HUMAN BODY 



1. Regions of the body. In man and in most other 

 mammals one can distinguish at least three regions ; namely, 

 the head, neck, and trunk. To the trunk are attached two 

 pairs of appendages ; namely, two arms and two legs, or, as 

 they are more often called in the descriptions of the lower 

 animals, the four legs. If the front wall of the trunk (com- 

 posed largely of skin and muscle) were removed, it would be 

 found that this region of the human body is divided into 

 an upper story or chest cavity (Fig. 1), and a lower story or 

 abdominal cavity. These two cavities are separated from 

 each other by a flexible partition called the diaphragm, 

 which is composed largely of muscle more or less in the form 

 of a dome. The chest and abdominal cavities, separated by 

 a diaphragm, are characteristic of all mammals. 



2. Organs of the body. 1 When we study the body more 

 closely, especially its interior, we find, in various regions, 

 parts that carry on special kinds of work (Fig. 2). Within 

 the chest cavity is the heart, which forces blood through the 



1 Each of the structures named in this paragraph should be demon- 

 strated on a manikin or a chart before the textbook lesson is as- 

 signed. While studying the lesson, the pupil should find in Fig. 2 

 each of the organs named. 



B 1 



