6 THE HUMAN BODY. 



The general plan on which, the Body is constructed. 

 When we desire to gain a general idea of the structural 

 plan of any object we examine, if possible, sections made 

 through it in different directions ; the botanist cuts the 

 stem of the plant he is examining lengthwise and cross- 

 wise, and studies the surfaces thus laid bare ; a geologist, 

 investigating the structure of any portion of the earth's 

 crust, endeavors to find exposed surfaces in canons, in 

 railway cuttings, and so forth, where he may see the strata 

 exposed in their natural relative positions ; and the archi- 

 tect draws plans which show to his clients sections of the 

 building which he proposes to erect for them ; so, also, the 

 best method of getting a good general idea of the way in 

 which the parts of the human body are put together is 

 to study them as laid bare by cuts made in different direc- 

 tions ; this gives us a general outline and the details may 

 be filled in afterwards. 



If the whole body were divided from the crown of 

 the head to the lower end of the trunk, and exactly in the 

 middle line, so as to separate it into right and left halves, 

 we should see something like Fig. 1, if we looked at the cut 

 surface of the right half. Such a section shows us, first, 

 that the body fundamentally consists of two tubes or cav- 

 ities, separated by a solid bony partition. The larger cav- 

 ity, I, c, known as the ventral or licemal cavity, lies on 

 the front side, and contains the greater part of the organs 



How do we start by preference to gain a knowledge of the struc- 

 tural plan of any mass of matter? Give examples. Apply to 

 the study of human anatomy. 



What should we see on examining the cut surface of a human 

 body divided into right and left halves? What organs lie in the 

 haemal cavity? What in the neural? How far does the haemal 

 cavity extend toward the head ? 



