144 THE WONDERFUL HOUSE THAT JACK HAS 



to the backbone, but only the upper seven are joined 

 to the sternum. The first seven pairs on this ac- 

 count are called true ribs. The eighth, ninth, and 

 tenth pairs are joined each to the one above and are 



The Thorax, showing Lungs and Heart. 



called false ribs. The eleventh and twelfth are not 

 fastened at all in front, and hence are named floating 

 ribs. 



On page 145 is shown the position of the strong 

 muscle called the diaphragm. The latter separates the 

 chest from the abdomen, A semielas,tic substance 



