104 NATURAL THEOLOGY. 



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 the fore-arm may be swinging upon its 

 hinge at the elbow, at the ver}'- time that the les- 

 ser 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 observable. 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 spitie, or back-bone, is a chain of joints 

 of very wonderful construction. A^arious, difficult, 

 and almost inconsistent offices were to be exe- 

 cuted by the same instrument. It was to be firm, 



