the will; while others are signs of emotion, over which we have a
very limited or imperfect control. The face serves for the lowest
animal enjoyment, and reflects the highest and most refined emotions.
Happily for our present inquiry, the nerves, which in other
parts of the frame are bound together for the convenience of
distribution to remote parts, are here distinct, and run apart from
each other, until they meet at their extremities.
On turning to the plate of the nerves of the face, and consulting
the explanation, it will be seen that there are two sets of nerves
running upon it. One nerve comes out just before the ear, and
spreads out to every part. Another nerve is not seen in its
course through the head, but its four branches are seen to come
out upon the face: the first above the eye, going to the forehead;
the second below the eye, sent to the nose and cheek; the third
branch coming out upon the chin, and the fourth before the ear.
The great nerve that comes out before the ear, and spreads over
the face, does not exist in any of the lower tribes of animals unless
the creature breathes by nostrils. When it exists, I have found
that it does not bestow sensibility as the other nerves do; that
when it is cut across, the sensibility of the skin is not diminished.
But if this nerve be cut across, the motions of the nostrils which
accompany the act of breathing immediately cease. On the contrary,
if the other nerves which come out upon the face, branches
of what is called the fifth pair, are divided, sensibility is destroyed;
and if the trunk of the same nerve be cut, the motion of the jaw is
lost; but the fine motions of the face, which accord and keep time
with the motions of the chest in breathing, whether awake or
asleep, continue unimpaired.
When a horse has run and pants and breathes hard, the nostrils
are alternately dilated and contracted, while the chest rises and
falls. So in a man, excited by exercise or passion, the shoulders
are raised at each inspiration, the muscles of the neck and throat
are violently drawn, and the lips and nostrils move in time with
the general action. Thus parts remote in situation are combined
in function, and when thus united in the act of respiration, it is by
means of distinct nerves appropriated to that office. The nerves
which perform this function come out from where the spinal
marrow joins the brain, and from thence they diverge to remote
parts: to the face, the windpipe, the neck and shoulders, the outside
of the chest, the diaphragm. The division of any one of these
nerves cuts off the part to which it is distributed from combining
in the act of respiration, without depriving it of sensibility, or impeding
the forcible action of its muscles when excited by other
nerves, or acting in the performance of some other function.
These nerves, from their principal function, I have distinguished
by the term respiratory nerves, since it is solely through them that
the muscles are excited to the act of breathing. But we are led to
inquire what other offices the organs of respiration, and the respira