THE HUMAN FliAAlE. 71 



radius plays into a socket, of the ulna ; while below, that is, 

 towards the wrist the radius finds the socket, and the ulna 

 the tubercle, A single bone in the fore-arm, with a ball- 

 and-socket joint at the elbow, which admits of motion in all 

 directions, might, in some degree, have answered the pur- 

 pose of both moving the arm and turning the hand. But 

 how much better it is accomplished by the present mechan- 

 ism any person may convince himself who puts the ease and 

 quickness with which he can shake his hand at the wrist 

 circularly — moving likewise, if he pleases, his arm at the 

 elbow at the same time — in competition with the compara- 

 tively slow and laborious motion with which liis arm can be 

 made to turn round at the shoulder by the aid of a ball-and- 

 socket joint. 



III. The S2nne, or backbone, is a chain of joints of very 

 wonderful construction. Various, difficult, and almost in- 

 consistent offices were to be executed by the same instru- 

 ment. It was to be firm, yet flexible — now I know no chain 

 made by art which is both these — for, by firmness, I mean 

 ixot only strength but stability : finn, to support the erect 

 position of the body ; Jlexible, to allow of the bending of the 

 trunk in all degrees of curvature. It was further also — 

 which is another and quite a distinct purpose from the rest — 

 to become a pipe or conduit for the safe conveyance from 

 the brain of the most important fluid of the animal frame, 

 that, namely, upon which all voluntary motion depends, the 

 spinal marrow ; a substance not only of the first necessity 

 to action, if not to life, but of a nature so delicate and ten- 

 der, so susceptible and so impatient of injury, as that any 

 unusual pressure upon it, or any considerable obstruction of 

 its course, is folloM^ed by paralysis or death. 



Now the spine was not only to furnish the main trunk 

 fo2 the passage of the medullary substance from the brain, 

 but to give out, in the course of its progress, small pipe? 

 therefrom, which, being afterwards indefinitely subdivided 

 laight, under the name of nerves, distribute this exquisitt 



