OF THE JOINTS. 221 



there is a happy provision, producing at once firm- 

 ness and mobihty. That is to say, when the limb 

 is thrown forward in walking or running, it is 

 loose, and capable of being freely directed ; so 

 that we plant it with every convenience to the ir- 

 regularity of ground : but when the body is car- 

 ried forward to be perpendicular over that limb, 

 it acquires, by the curious adjustment of the bones, 

 a firmness equal to that of a post. Again ; when 

 the body is still further thrown forward, and the 

 limb is disencumbered of the weight of the body, 

 the joints are let loose so as to be bent easily, and 

 to obey the action of the muscles. 



20* 



