THE HUMAN FRAME 83 



well as action . With a capacity for motion in all directions 

 indeed, as at the shoulder, but not in any direction to the 

 same extent as in the arm, was to be united stability, or re- 

 sistance to dislocation. Hence the deeper excavation of the 

 socket, and the presence of a less proportion of cartilage upon 

 the edge. 



The suppleness and pliability of the joints we every mo- 

 ment experience ; and the firmness of animal articulation, 

 the property we have hitherto been considering, may be 

 judged of from this single observation, that, at any given 

 moment of time, there are millions of animal joints in com- 

 plete repair and use, for one that is dislocated ; and this, 

 notwithstanding the contortions and wrenches to which the 

 limbs of animals are continually subject. 



11. The joints, or rather the ends of the bones which 

 form them, display also, in their configuration, another use. 

 The nerves, bloodvessels, and tendons, which are necessary 

 to the life, or for the motion of the limbs, must, it is evident, 

 in their way from the trunk of the body to the place of their 

 destination, travel over the movable joints ; and it is no less 

 evident that, in this part of their course, they will have, 

 fi'om sudden motions, and from abrupt changes of curvature, 

 to encounter the danger of compression, attrition, or lacera- 

 tion. To guard fibres so tender against consequences so in- 

 jurious, their path is in those parts protected with peculiar 

 care, and that by a provision in the figure of the bones them- 

 selves. The nerves which supply the fore-arm, especially 

 the inferior cubital nerves, are at the elbow conducted, by 

 a kind of covered way, between the condyles, or rather under 

 the inner extuberances of the bone which composes the up- 

 per part of the arm.* At the knee, the extremity of the 

 thigh-bone is divided by a sinus, or cUff^ into fwo heads or 

 protuberances ; and these heads on the back part stand out 

 beyond the cylinder of the bone. Through the hollow which 

 lies betw^een the hind parts of these two heads — that is to 

 * Chcselden's Anat., p. 255, ed. 7. 



