NATURAL THEOLOGY. 81 



precisely the mechanism which is used in the motions 

 of the head ! 



T. You can turn the telescope, however, entirely 

 round ; but you are aware, it is not the same with the 

 head. The head has only a certain degree of motion 

 from side to side ; and this is confined to a very small 

 compass, though sufficient for the purpose ; suffi- 

 cient, that is, with the motion of the eyes, which 

 nearly completes the circle. But for this limitation 

 of the motion, I need not tell you the spinal marrow 

 would have been in danger of being twisted or com- 

 pressed. A most artificial contrivance is introduced, 

 which prevents this danger can you describe it? 



A.. There are two ligaments, small, but exceed- 

 ingly strong, which are attached to the joint in such a 

 manner, as to allow it sufficient play, but not to admit 

 of any motion beyond a certain extent. They are 

 called the moderator ligaments, from a Latin word 

 signifying to moderate or check. 



B. Then, if I understand it, when we attempt to 

 turn the head upon either side farther than would be 

 safe, one of these cords immediately arrests the mo- 

 tion, like a check rope, such as we sometimes see em- 

 ployed on gates, doors, &c., and acting exactly upon 

 the same principle. 



T. But there is another circumstance which it be- 

 longs to our present purpose to understand. You 

 have seen that the structure of the skull is admirably 

 adapted to preserve the brain from being jarred. Is 

 there any harmony of provision for the same purpose, 

 in the structure of the spine, that is, of the support on 

 which the brain immediately rests ? 



