422 Mr. Bell’s experiments on the structure 
In all the intermediate emotions between these extremes, the 
varieties of expression in the face are produced by the oppo- 
sition of the two powers affecting the same muscles ; the one 
is a voluntary power, by which we restrain the features and 
conceal emotion ; the other is an involuntary power, which 
cannot be always controuled, but which will sometimes have 
sway and mingle its influence, 
* 
Conclusion. 
When the account of the nerves of the throat, neck, and 
chest, shall be laid before the Royal Society, as those of the face 
have now been, and when a comparison shall be made of the 
varieties in nerves corresponding with the changes in the 
mechanism of respiration in different animals, a juster esti- 
mate may be formed of the importance of these observations. 
Then the same distinctions of structure and function, which 
are made manifest in the nerves of the face, will be observed 
in nerves which take an extensive course through the body. 
We shall be able to distinguish and separate the nerves of 
respiration, amidst the apparent intricacy of the general 
system. By cutting across these nerves of respiration, we 
shall find it possible successively to stop the motions of the 
several parts, which unite in the act of respiration; not only 
to stop the motion of the diaphragm, but the motions of the 
side, of the shoulder, of the larynx or the pharynx, by cutting 
their respective respiratory nerves. When this is done, they 
will be left in the exercise of their other functions through 
their other nerves, and still alive to other excitements, and 
capable of performing the voluntary motions, though dead to 
the influence of the heart and lungs. 
