128 NATURAL THEOLOGY. 



the slipping and sliding of the loose cartilages, 

 though it be probably a small and obscure change, 

 humoured the motion at the end of the thigh-bone, 

 under the particular configuration which was neces- 

 sary to be given to it for the commodious action of 

 the tendons (and which configuration requires w^hat 

 he calls a variable socket, that is, a concavity, the 

 lines of which assume a different curvature in dif- 

 ferent inclinations of the bones.)^" 



V. We have now done with the configuration : 

 but there is also in the joints, and that common to 

 them all, another exquisite provision manifestly 

 adapted to their use, and concerning which there 

 can, I think, be no dispute, namely, the regular sup- 

 ply of a mucilage, more emollient and slippery than 

 oil itself, which is constantly softening and lubricat- 

 ing the parts that rub upon each other, and thereby 



^2 This is not explained with our author's usual clearness. The 

 lower head of the thigh-bone, which rests upon the shin-bone or 

 tibia, is not the segment of a regular circle. When we stand with 

 the knees straight, the thigh-bone rests with a broad surface, and 

 the convexity is principally on the back part. Such an irregularity 

 would make a very imperfect and jarring hinge-joint on any con- 

 figuration that could be given to the corresponding surface of the 

 tibia. Therefore these cartilages intervene ; and, being possessed 

 of considerable elasticity, and so connected with the bone as to 

 shift their place a little, they accommodate themselves, whether the 

 flatter end or the more convex part of the articulating surface of 

 the bone be presented to them ; and there is this advantage, that, 

 in standing, when the Aveight on the joint is greatest, the thigh- 

 bone has a more extensive, and consequently a more secure basis, 

 at the same time that the motion of the joint as a hinge is perfect, 



