28 



OUR BODIES AND HOW WE LIVE 



a heavy weight and yet bend like rubber. It is a tapering 

 pile of odd-shaped bones, so admirably planned and so 

 wonderfully put together, that the delicate brain resting 

 upon it, and the spinal cord hidden within its bony canal, 

 are not often hurt. 



The most daring acrobat rarely breaks the bones of his 

 spine or puts them out of place. It is not an uncommon 

 thing to see show people bend their backs until they can 



put their heads on the 

 ground, or clasp their 

 legs around their necks. 



Experiment 9. To illus- 

 trate the movement of torsion 

 in the spine. Sit upright with 

 the back and shoulders well 

 applied against the back of a 

 chair. Note* that the head 

 and neck can be turned as 

 much as 60 or 70. Now 

 bend forward so as to let the 

 lumbar vertebrae come into 

 play, and the head can be 

 turned 30 farther. 



44. The Ribs. The 

 ribs are long, flat, and 

 curved bones which bend 

 round the chest somewhat like the hoops of a barrel. There 

 are twenty-four ribs, twelve on each side. 



The ribs are joined to the backbone behind, and most of 

 them are joined in front, directly or indirectly, to a flat, 

 narrow bone, which is shaped somewhat like an ancient 

 sword or dagger. It forms the middle front wall of the 

 chest and is called the sternum, or breastbone, 



FIG. 19. Thorax. 

 Anterior view. 



