12 STRUCTURE OF THE HUMAN BODY 



the skeleton lies entirely outside of the softer tissues. 

 In vertebrates, on the contrary, the skeleton is entirely 

 covered by the flesh. 1 By this arrangement, the skeleton 



FIG. 8. Animal with external skeleton (crab). 



supports and protects the softer tissues and is in turn 

 protected by them. 



Arrangement of bones and organs. The human 

 skeleton consists of a large number of bones (about 

 208) so arranged and distributed in and about the 

 body's central axis, the spinal column, as to be alike 

 on both sides, that is, bilaterally symmetrical. The two 

 sides are, however, complements of each other in shape 

 and position, that is, rights and lefts. Most of the soft 

 tissues are also symmetrically arranged in pairs, as for 

 example the muscles, blood-vessels, nerves, lungs and 

 kidneys. The exceptions to this are such organs as the 

 heart, stomach, liver and intestines, which are irregular 

 in shape and not in pairs. 



1 The turtle, although a vertebrate, has its backbone and ribs 

 so blended that they form a shell which in certain particulars 

 resembles an outside skeleton. 



