NATURAL THEOLOGY. 107 



Stability ; the number of parts, and consequent 

 frequency of joints, its flexibility. Which flexi- 

 bility, we may also observe, varies in difterent parts 

 of the chain ; is least in the back, where strength 

 more than flexure is wanted ; greater in the loins, 

 which it was necessary should be more supple 

 than the back ; and greatest of all in the neck, for 

 the free motion of the head. Then, secondly, in 

 order to aflbrd a passage for the descent of the 

 medullary substance, each of these bones is bored 

 through in the middle, in such a manner as that, 

 when put together, the hole in one bone falls into 

 a line and corresponds with the holes in the two 

 bones contiguous to it. By which means the per- 

 forated pieces, when joined, form an entire, close, 

 uninterrupted channel, at least whilst the spine is 

 upright and at rest. But as a settled posture is 

 inconsistent with its use, a great difficulty still re- 

 mained, which was to prevent the vertebrae shift- 

 ing upon one another, so as to break the line of 

 the canal as often as the body moves or twists, 

 or the joints gaping externally whenever the body 

 is bent forward and the spine thereupon made to 

 take the form of a bow. These dangers, which 

 are mechanical, are mechanicallyprovided against. 

 The vertebra3, by means of their processes and 

 projections, and of the articulations which some 

 of these form with one another at their extremi- 

 ties, are so locked in and confined as to maintain, 

 in what are called the bodies or broad surfaces of 

 the bones, the relative position nearly unaltered, 



