CHAPTER XXXIV 

 THE FRAMEWORK OF THE BODY 



201. The Skeleton. From the fact that the simplest 

 animals have no skeleton, we perceive that the possession of 

 such a structure is not an essential characteristic of animal 

 life, though, since all the higher types possess something of the 

 kind, it apparently plays a part of some importance in the 

 animal body. The first skeletons were external and were 

 represented by such structures as the shell of the clam, the 

 hard outer parts of the lobster and crayfish, and the horny 

 covering of beetles and other insects. An internal skeleton 

 is found only in the group called vertebrates, and it is only 

 in this group that true bones occur. Man being the highest 

 representative of this latter group, of course, has one of the 

 most highly developed of skeletons. 



202. Arrangement of the Skeleton. The skeleton serves as 

 the framework of the body, somewhat analogous to the wood 

 and bast of plants. Its chief function is to form attachments 

 for the muscles and thus to aid in producing motion, though 

 it also serves to give shape and strength to the body and to 

 protect the more delicate organs. A fundamental pattern 

 may be seen in the skeletons of all vertebrates, though 

 variously modified to meet individual needs. There is first 

 of all an axis consisting of a number of joints or vertebrce which 

 we commonly call the spine or back bone. In man there are 

 thirty-three of these vertebrae, though in adult life the last 

 nine are fused together into what appear to be two bones. 

 In the lower animals, these bones, often with others, form the 

 tail. At the opposite end of the axis are twenty-two irregular 



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