DOI Page / Citation link:
https://doi.org/10.11588/diglit.4812#0105
NERVOUS SYSTEM. 95
CHAPTER XXVIII.
Of the Manner and Causes os the Actions of the Muscles^
|"N the jirji place, we know that by sar the greater number os motions
we perform seem to be regulated by the will; and hence the mufcles,
which persorm these motions, have been very generally called voluntary
muscles.
Other motions seem to be spontaneous. In some of thefe, we are sen-
sible os a stimulus, or uneafiness, which precedes the motion; in others,
this stimulus is overlooked or not to be selt. In almoft none os them are
we conscious that our will interposes in directing the mode os aclion. Nay,
it is evident, that we cannot suppose that the will interposes in directing
the mode; because, not only the muscles themselves, but the essects os
them, are unknown to us*
To illuftrate this subjecl:, I mall briessy enumerate the chies spontaneous
motions os animals, in the order in which I apprehend they ought to be ar-
ranged when we mean to investigate their causes-
SECT. I.
I shall begin with thofe examples in which the irritation that produces
the motion is at a diftance srom the muscles' which persorm it, and, by
degrees* proceed to those in which the adive organ is directly stimulated.
1. The iris is contracted in proportion to the quantity of light which
impresses the retina, is the retina is in a sound state-
But
CHAPTER XXVIII.
Of the Manner and Causes os the Actions of the Muscles^
|"N the jirji place, we know that by sar the greater number os motions
we perform seem to be regulated by the will; and hence the mufcles,
which persorm these motions, have been very generally called voluntary
muscles.
Other motions seem to be spontaneous. In some of thefe, we are sen-
sible os a stimulus, or uneafiness, which precedes the motion; in others,
this stimulus is overlooked or not to be selt. In almoft none os them are
we conscious that our will interposes in directing the mode os aclion. Nay,
it is evident, that we cannot suppose that the will interposes in directing
the mode; because, not only the muscles themselves, but the essects os
them, are unknown to us*
To illuftrate this subjecl:, I mall briessy enumerate the chies spontaneous
motions os animals, in the order in which I apprehend they ought to be ar-
ranged when we mean to investigate their causes-
SECT. I.
I shall begin with thofe examples in which the irritation that produces
the motion is at a diftance srom the muscles' which persorm it, and, by
degrees* proceed to those in which the adive organ is directly stimulated.
1. The iris is contracted in proportion to the quantity of light which
impresses the retina, is the retina is in a sound state-
But