M OF MECHAXICAL ARRANGEMENT 



or upper arm at the elbow, or both to the hand at the wrisfi^ 

 the thing could not have been done. The first was to be 

 at liberty at one end, and the second at the other : by which 

 means the two actions may be performed together. The 

 great bone, which carries tlie fore-arm, may be swinging 

 upon its hinge at the elbow, at the very same time, that 

 the lesser bone, which carries the hand, may be turning 

 round it in the grooves. The management also of these 

 grooves, or rather of the tubercles and grooves, is very ob- 

 servable. The two bones are called the radius and the 

 ulna. Above, i. e. towards the elbow, a tubercle of the 

 radius plays into a socket of the ulna ; whilst below, i. e. 

 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 

 purpose, of both moving the arm, and turning the hand. 

 But how much better it is accomplished by the present me- 

 chanism, 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 

 comparatively slow and laborious motion, with which his 

 arm can be made to turn round at the shoulder, by the aid 

 of a ball and socket joint. 



III. The spine or back bone is a chain of joints of very 

 wonderful construction. (PI. IX. fig. 1, 2.) Various, diffi- 

 cult, and almost inconsistent offices were to be executed by 

 the same instrument. It was to be firm, yet flexible, (now 

 I know no chain made by art, which is both these ; for 

 by firmness I mean not only strength, but stability ; frrn, 

 to support the erect position of the body ; flexible, 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 con- 

 veyance from the brain of the most important fluid* of the 

 animal frame, that, namely, upon which all voluntary mo- 

 tion depends, the spinal marrow ; a substance not only of 



* It seems proper to remark here, that the form of expression made 

 use of in this case implies what is not strictly true. The spinal mar- 

 row, or more properly the Spinal nerve, is not a fluid but a solid cord 

 extending Irom the brain down through the canal of the spine, from 

 which branches are distributed to all parts of the body. Dr. Paley in 

 this instance probably had in view the animal spirits, a subtle fluid, 

 which was formerly believed to be seated in the brain, and carried 

 tlirough the nerves to the different parts. -E*^- 



