VERTEBRAL COLUMN. 389 



to all the large muscles which act upon these 

 bones as levers, and also to those which move 

 the trunk itself. 



If this column had been perfectly rigid, the 

 whole frame- work would have been exposed to 

 inconvenience and even danger, amidst the 

 shocks it must encounter during all the quick 

 and sudden movements of the body. Not only 

 must its mechanism be framed to sustain these 

 shocks, but also to accommodate itself to various 

 kinds of flexions, and twistings of the trunk. 

 While these objects are provided for, care must 

 at the same time be taken that the spinal mar- 

 row it encloses shall, amidst all these motions, 

 remain secure from pressure ; for so delicate is 

 its structure that the least degree of compression 

 would at once interrupt its functions, and lead 

 to the most fatal consequences. A safe passage 

 is likewise to be afforded to the nerves, which 

 issue from the spinal marrow, at certain inter- 

 vals, on each side throughout its whole length. 



No where has mechanical art been more con- 

 spicuously displayed than in the construction of 

 a fabric capable of fulfilling these opposite, and 

 apparently incompatible functions. The prin- 

 cipal difficulty was to combine great strength 

 with sufficient flexibility. This we find accom- 

 plished, first, by the division of the column into 

 a great number of pieces, each of which being 

 locked in with the two adjoining pieces, and 



