,348 THE MECHANICAL FUNCTIONS. 



functions, and lead to the most fatal consequences. 

 A safe passage is likewise to be afforded to tlie 

 nerves, which issue from the spinal marrow, at 

 certain intervals, on each side, throughout its whole 

 length. 



No where has mechanical skill been more con- 

 spicuously displayed than in the construction of 

 a fabric capable of fulfilling these opposite, and 

 apparently incompatible functions. The principal 

 difficulty was to combine great strength with suffi- 

 cient flexibility. This we find accomplished, 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 tightly braced by con- 

 necting ligaments, is allowed but a very small 

 degree of flexion at the point of junction. This 

 slight flexion at each single joint, however, by 

 becoming multiplied along the series, amounts to 

 a considerable degree of motion in the whole 

 column. 



The broad basis of each bone is connected with 

 the next, not by a joint, but by a plate of equal 

 breadth (m, m, Figures 178 and 179), composed of 

 a peculiar substance, intermediate in its texture to 

 ligament and cartilage, and possessing in a remark- 

 able degree the qualities of toughness and adhesion, 

 united with compressibility and elasticity. By 

 yielding for a certain extent to a force tending to 

 bend it to either side, it diminishes the quantity of 

 motion which would otherwise have been required 

 in each individual joint ; and by acting, at the same 

 time, as a spring, it softens all the jars and con- 

 cussions incident to violent action : for we find that, 

 however the spine may be bent, no chasm is left by 



