404 Mr. Bell's experiments on the structure 
frame, the nerves are extremely simple; they consist of two 
cords running in the length of the body, with branches going 
off laterally to the several divisions of the frame. And here 
no intricacy is to be seen, no double supply of nerves is to be 
observed, but each portion of the frame has an equal supply ; 
and the central line of connection is sufficient to combine the 
actions of the muscles, and to give them the concatenation 
necessary to locomotion. 
There is the same uniform and symmetrical system of nerves 
in the human body as in the leech or worm ; although obscured 
by a variety of superadded nerves. These additional nerves 
belong to organs, which, tracing the orders of animals upward, 
are observed gradually to accumulate until we arrive at the 
complication of the human frame. These nerves, additional 
and superadded to the original system, do not destroy, but only 
obscure that system ; and accordingly, when we separate cer- 
tain nerves, the original system of simple constitution is pre- 
sented even in the human body. 
The nerves of the spine, the tenth or sub-oc.cipital nerve, 
and the fifth or trigeminus of the system of Willis, constitute 
this original and symmetrical system. All these nerves agree 
in these essential circumstances ; they have all double origins ; 
they have all ganglia on one of their roots ; they go out late- 
rally to certain divisions of the body ; they do not interfere to 
unite the divisions of the frame ; they are all muscular nerves, 
ordering the voluntary motions of the frame ; they are all 
exquisitely sensible ; and the source of the common sensibility 
of the surfaces of the body : when accurately represented on 
paper, they are seen to pervade every part ; no partis without 
them ; and yet they are symmetrical and simple as the nerves 
of the lower animals. 
