26 



THE FRAMEWORK OF THE BODY 



of as the "back-bone," as if it were a single bone, while, in 

 reality, it is composed of a chain of twenty-six small bones, 

 called vertebras. The spinal column is a wonderful piece of 

 mechanism. It not only connects the important cavities of the 

 body, as has already been shown, but 

 also, itself forms a canal, which contains 

 the spinal cord. The joints of the ver- 

 tebrae are remarkable for the thick layers 

 of cartilage which separate the adjacent 

 surfaces of bone. The amount of motion 

 between any two of these bones is not 

 great ; but these little movements, taken 

 together, admit of very considerable flexi- 

 bility, in several directions, without en- 

 dangering the supporting power of the 

 column. 



12. The abundant supply of inter- 

 vertebral cartilage has another impor- 

 tant use, namely, it adds greatly to the 

 elasticity of the frame. It is due, in 

 part, to this elastic material, and in part 

 to the frequent curves of the spine, that 

 the brain and other delicate organs are 

 not more frequently injured by the shock 

 of sudden falls or missteps. During the 

 day, the constant pressure upon these 

 joints, while the body is erect, dimin- 

 ishes the thickness of the cartilages ; so 

 that a person is not so tall in the even- 

 ing as in the morning. The effects of 

 this compression pass away when the 

 body is in a reclining posture. (Read 

 Note 7.) 



7. Some Causes of Curvature of the Spine. " Much as horse-riding 

 is valued on account of the healthful character of its exercise, yet an over- 

 indulgence by young ladies owing to the oblique position in which the 



Sacrum 



Coccygis 



FIG. 10. THE SIMNAI 

 Co LOIN 



12. Elasticity of the frame? Protection of the brain from shocks? Tallness of persons ? 

 Effects of reclining ? 



