28 ANIMAL MECHANICS 



Such would be the effect on the spine if it 

 stood upright, one bone perpendicular to another ; 

 for then the weight would bear equally ; the spine 

 would yield neither to one side nor to the other; 

 and, consequently, there would be a resistance 

 from the pressure on all sides being balanced. 

 We therefore see the great advantage resulting 

 from the human spine being in the form of an 

 italic s. It is prepared to yield in the direction 

 of its curves ; the pressure is of necessity more 

 upon one side of the column than on the other ; 

 and its elasticity is immediately in operation with- 

 out a jerk. It yields, recoils, and so forms the 

 most perfect spring ; admirably calculated to carry 

 the head without jar, or injury of any kind. 



The most unhappy illustration of all this is the 

 condition of old age. The tables of the skull are 

 then consolidated, and the spine is rigid : if an 

 old man should fall with his head upon the car- 

 pet, the blow, which would be of no consequence 

 to the elastic frame of a child, may to him prove 

 fatal ; and the rigidity of the spine makes every 

 step which he takes vibrate to the interior of the 

 head, and jar on the brain. 



We have hinted at a comparison betwixt the 

 attachment of the spine to the pelvis and the in- 

 sertion of the mast of a ship into the hull. The 

 mast goes directly through the decks without 

 touching them, and the heel of the mast goes into 



