80 NATURAL THEOLOaY. 



meiil like membrane, rising from, the receiving bones, and 

 inserted all round the received bones a little below their 

 heads, encloses the jomt on every side. This membrane ties, 

 confines, and holds the ends of the bones together, keeping 

 the corresponding parts of the joints — that is, the relative 

 convexities and concavities — in close application to each 

 other. 



For the ball-and-socket jomt, besides the membrane 

 already described, there is in some important joints, as an ad- 

 ditional secm-ity, a short, strong, yet flexible ligament, insert- 

 ed by one end into the head of the ball, by the other, into 

 the bottom of the cup ; which ligament keeps the two parts 

 of the joint so firmly in their place, that none of the motions 

 which the limb naturally performs, none of the jerks and 

 twists to which it is ordinarily liable, nothing less indeed 

 than the utmost and the most unnatural violence, can pull 

 them asmider. It is hardly imaginable how great a force is 

 necessary even to stretch, still more to break, this ligament : 

 yet so flexible is it, as to oppose no impediment to the sup- 

 pleness of the joint. By its situation also, it is inaccessible 

 to mjury from sharp edges. As it cannot be ruptured, such 

 is its strength, so it cannot be cut, except by an accident 

 which would sever the limb. If I had been permitted to 

 frame a proof of contrivance such as might satisfy the most 

 distrustful inquirer, I know not whether I could have chosen 

 an example of mechanism more unequivocal or more free 

 from objection, than this Hgament. Nothing can be more 

 mechanical ; nothing, however subservient to the safety, les9 

 capable of being generated by the action of the joint. 1 

 would particularly solicit the reader's attention to this pro- 

 vision, as it is found in the head of the thigh-hone — to its 

 strength, its structure, and its use. It is an instance upon 

 which Hay my hand. One single fact, weighed by a mind 

 in earnest, leaves oftentimes the deepest impression. Foi 

 the purpose of addressing difTerent understandings and dif 

 ferent apprehensions — for the purpose of sentiment — for the 



