sensorium residing in the muscles or organs of sense, in consequence of the
appulses of external bodies.

SENSATION is an exertion or change of the central parts of the sensorium,
or of the whole of it, _beginning_ at some of those extreme parts of it,
which reside in the muscles or organs of sense.

VOLITION is an exertion or change of the central parts of the sensorium, or
of the whole of it, _terminating_ in some of those extreme parts of it,
which reside in the muscles or organs of sense.

ASSOCIATION is an exertion or change of some extreme part of the sensorium
residing in the muscles or organs of sense, in consequence of some
antecedent or attendant fibrous contractions.

3. These four faculties of the animal sensorium may at the time of their
exertions be termed motions without impropriety of language; for we cannot
pass from a state of insensibility or inaction to a state of sensibility or
of exertion without some change of the sensorium, and every change includes
motion. We shall therefore sometimes term the above described faculties
_sensorial motions_ to distinguish them from _fibrous motions_; which
latter expression includes the motions of the muscles and organs of sense.

The active motions of the fibres, whether those of the muscles or organs of
sense, are probably simple contractions; the fibres being again elongated
by antagonist muscles, by circulating fluids, or sometimes by elastic
ligaments, as in the necks of quadrupeds. The sensorial motions, which
constitute the sensations of pleasure or pain, and which constitute
volition, and which cause the fibrous contractions in consequence of
irritation or of association, are not here supposed to be fluctuations or