6Q OF 3IECHAN1CAL ARRANGEMENT 



the calves of the legs before : and there would have been 

 great confinement by restraining the motion of the thighs 

 to one plane. The disadvantage would not have been 

 less, if the joints at the hip and the knee had been both of 

 the same sort ; both balls and sockets, or both hinges : yet 

 wiiy, independently of utility, and of a Creator who con- 

 sulted that utility, should the same bone (the thigh bone) 

 be rounded at one end, and channelled at the other 1 



The hinge joint is not formed by a bolt passing through 

 the two parts of the hinge, and thus keeping them in their 

 places ; but by a different expedient. A strong, tough, 

 parchment-like membrane, rising from the receiving bones, 

 and inserted all round the received bones a little below 

 their heads, encloses the joint on every side. This mem- 

 brane ties, confines, and holds the ends of the bones to- 

 gether ; keeping the corresponding parts of the joint, i. e. 

 the relative convexities and concavities in close application 

 to each other.* 



For the hall and socket joint, beside the membrane al- 

 ready described, there is in some important joints, as an 

 additional security, a short, strong, yet flexible ligament, 

 inserted, by one end into the head of the ball, by the oth- 

 er 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 vio- 

 lence, can pull them asunder. [Plate XL fig. 1.] It is 

 hardly indeed 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 impedient to the suppleness of 

 the joint.f By its situation also, it is inaccessible to injury 

 from sharp edges. As it cannot be ruptured such is its 



* This membrane is the capsular, or bursal ligament, common to 

 every moveable joint. It certainly connects the bones together, but 

 does not possess much strength : its chief use is to produce and pre- 

 serve the synovia in the part where it is required. The security and 

 strength of the hinge joint depends on certain ligaments called lateral 

 ligaments, and the tendons of those muscles which pass over it. In 

 the particular instance of the knee, from its being the largest joint in 

 the body, there is, as we shall presently find, an additional contrivance 

 to prevent dislocation. Paxton. 



t This ligament is also common to all quadrupeds, even in the more 

 large and unwieldly, as the Hippopotamus and Rhinoceros — it is want- 

 ing in the Elephant only, whose limbs, ill qualified for active move- 

 ments, do not seem to require this se'^urity to the joint. Paxton. 



