and functions of the nerves. 415 
where the nerves were entire, was curled up with the peculiar 
expression of sneezing ; but on the other side, where the 
nerve was divided, the face remained quite relaxed, although 
the branches of the fifth pair and the sympathetic were en- 
tire. The respiratory nerve of one side of the face of a dog 
being cut, the same effect was produced ; the action of sneez- 
ing was entirely confined to one side of the face. 
These last experiments show, that the peculiar expression 
in sneezing, results from an impression on the respiratory 
nerves, and that the muscles of the face are drawn into sym- 
pathy solely by the influence of the respiratory nerve of the 
face. 
There is no part of the nervous system where the anatomy 
has been more negligently consulted in forming our physio- 
logical opinions, than in what regards the office of the sympa- 
thetic nerve. The connections of this nerve, or rather system 
of nerves, being universal, it has been supposed that it was 
the chord through which the relations of the eye, nose, face, 
throat, diaphragm, &c. were established ; whereas the com- 
bination is effected solely through those nerves which, from 
their grand or leading function, I have called the respiratory 
nerves. 
It has been presumed, that the act of smiling is peculiar to 
the human countenance, and that in no other creature can 
there arise that state of enjoyment which produces this dis- 
tinguishing character of the human face, the expression of 
benevolence, or of the enjoyment of the ridiculous. But every 
one must have observed how near the approach is to this 
expression, in a dog when he fawns on his master, and leaps 
and twists his body and wags his tail, while, at the same time. 
