of the fibres of the facial nerve are acted on. Of the cause of this
we are quite ignorant."

[15] `De la Physionomie,' pp. 12, 73.

[16] `Mecanisme de la Physionomie Humaine,' 8vo edit. p. 31.

[17] `Elements of Physiology,' English translation, vol. ii. p. 934.

No doubt as long as man and all other animals are viewed
as independent creations, an effectual stop is put to our
natural desire to investigate as far as possible the causes
of Expression. By this doctrine, anything and everything can
be equally well explained; and it has proved as pernicious with
respect to Expression as to every other branch of natural history.
With mankind some expressions, such as the bristling of the hair under
the influence of extreme terror, or the uncovering of the teeth under
that of furious rage, can hardly be understood, except on the belief
that man once existed in a much lower and animal-like condition.
The community of certain expressions in distinct though allied species,
as in the movements of the same facial muscles during laughter by man
and by various monkeys, is rendered somewhat more intelligible,
if we believe in their descent from a common progenitor.
He who admits on general grounds that the structure and habits
of all animals have been gradually evolved, will look at the whole
subject of Expression in a new and interesting light.

The study of Expression is difficult, owing to the movements
being often extremely slight, and of a fleeting nature.
A difference may be clearly perceived, and yet it may be impossible,