DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.18825#0128
J02 PROPORTIONS OF THE HEAD. [lECT. v.
becomes dangerous; and therefore the'sg are pro-
tected with extraordinary a tention. The Eye is
partly secured, and as it were fortified, by the form
and projection of the surrounding features, whose
solidity may resist violent attacks ; and partly by
those curious curtains the eye-lids, whose instinctive
attention is too alert and watchful for every inimi-
cal intruder.
The ball of the eye floats with great liberty in
a kind of oil which lubricates its surface, and fa-
cilitates its motion. The iris or ring of the eve.
is centrically situated in the cornea, which by pro-
jecting a little, acquires a more extensive view of
surrounding objects. In the centre of the iris is the
pupil, an orifice through which the rays of light
pass to the internal humours, where they are con-
verged, and collected into a focus; thereby depict-
ing the image of external objects very clearly and
powerfully on the expansion of the optic nerve,
which here lines the internal surface, and which, be-
ing spread into a kind of most curious net-work, is
called the retina. Lest the action of the rays in a
focus should be too strong for the retina to bear, the
pupil has a power of excluding supernumerary ravs
of light. This curious part, by a most admirable
contrivance, possesses the faculty of contracting or
dilating itself, according to circumstances : in a
strong light, which might otherwise be offensive, or
injurious, its orifice contracts, so as to admit no
greater quantity of light than is convenient, but the
jnternal parts enjoy that moderation which is neces-
sary to the comfortable discharge of their office : in
the
becomes dangerous; and therefore the'sg are pro-
tected with extraordinary a tention. The Eye is
partly secured, and as it were fortified, by the form
and projection of the surrounding features, whose
solidity may resist violent attacks ; and partly by
those curious curtains the eye-lids, whose instinctive
attention is too alert and watchful for every inimi-
cal intruder.
The ball of the eye floats with great liberty in
a kind of oil which lubricates its surface, and fa-
cilitates its motion. The iris or ring of the eve.
is centrically situated in the cornea, which by pro-
jecting a little, acquires a more extensive view of
surrounding objects. In the centre of the iris is the
pupil, an orifice through which the rays of light
pass to the internal humours, where they are con-
verged, and collected into a focus; thereby depict-
ing the image of external objects very clearly and
powerfully on the expansion of the optic nerve,
which here lines the internal surface, and which, be-
ing spread into a kind of most curious net-work, is
called the retina. Lest the action of the rays in a
focus should be too strong for the retina to bear, the
pupil has a power of excluding supernumerary ravs
of light. This curious part, by a most admirable
contrivance, possesses the faculty of contracting or
dilating itself, according to circumstances : in a
strong light, which might otherwise be offensive, or
injurious, its orifice contracts, so as to admit no
greater quantity of light than is convenient, but the
jnternal parts enjoy that moderation which is neces-
sary to the comfortable discharge of their office : in
the