COVERING OF THE HOUSE. 115 



It is, in fact, a thin but tough cartilage. There 

 is a plain reason for this periosteum being used. 

 The frames of houses, &c., are made to stand 

 firmly ; they are not intended for motion ; but 

 the frame, and almost every part of the human 

 body, is made to move. But where there is 

 motion, it is desirable that the parts should be 

 rounded as much as possible, and every possi- 

 ble pains taken to prevent friction or wearing. 



After every bone * is covered over with this 

 thin substance, we have next the muscles and 

 tendons. It is the muscles generally, which 

 give soundness and beauty to the human body 

 and limbs. A large number of them are 

 situated on the bones, especially the long 

 bones, but some are extended between them. 

 The bones are generally smallest in the middle, 



* Or rather eveiy bone except the teeth. The 

 teeth, where they stand out of the gums, are covered 

 with enamel. A thin membrane like the periosteum, 

 would do no good, as it would soon wear out in 

 eating. The ends of the bones also, where they rub 

 against each other I mean at the joints are cov- 

 ered with a white elastic substance, which is not 

 exactly like the periosteum. 



