The Eye in its Relation to Health
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By Chalmer Prentice, M.D.
Chicago, A.C. McClurg & Company, 1895
Transcription (c) A. Wik, 2004

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        | Chapter XII |  pages 171-173
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								171

THE superior oblique muscle receives its nerve-
supply through the Fourth Cranial nerve;
the external rectus, through the Sixth; the supe-
rior, inferior, internal rectus, both obliques and
the ciliary, through the Third.
  That various parts receive their nerve-supply
from the same nerve does not imply that their
functions are necessarily similar, or that the gov-
erning nerve-centers are in the same locality; for
two fibrilla in a nerve, lying side by side, may
have the most widely separate origin possible in
the nerve-centers.
  Considered individually, the actions of the
long muscles of the eye are as follows:  The ex-
ternal rectus turns the eye outward; the internal
inward; the superior, upward and slightly inward
with a tortional movement of the upper aspect of
the eye toward the nose.  The inferior moves the
eye downward, slightly inward with a slight tor-
tion of the upper aspect of the eye from the nose.
The superior oblique makes a tortion of the upper
aspect of the eye toward the nose, with a slight
movement of the optic axes outward and down-
ward; the inferior oblique produces tortion of

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the upper aspect from the nose, with a small
tendency to turn the optic axes outward and
upward.
  Considered relatively, there are four antagon-
istic sets of muscles:  First, the superior and
inferior recti; second, the external and internal;
third, the superior and inferior obliques; fourth,
the superior and inferior recti as antagonized by
the superior and inferior obliques.  The latter set
slightly diverges the optic axes, and the former
set slightly converges them.
  There are six sets of synchronously acting
muscles:  First, the superior recti turn both eyes
upward; second, the inferior recti move them
downward; third, the right external and left in-
ternal recti turn both eyes to the right; fourth,
the left external and right internal recti turn both
eyes to the left; fifth, the superior and inferior
obliques of the right eye, acting together, in con-
nection with the superior and inferior recti of the
left eye, have a tendency to turn both eyes slightly
to the right; sixth, the superior and inferior ob-
liques of the left eye, acting synchronously with
the superior and inferior recti of the right eye,
turn the eyes slightly to the left.
  A still further secondary action takes place as
follows:  When the eye is turned upward so that
the relative equator of the eye-ball is thrown
below the parallelism of the internal and external

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recti, a contraction of these muscles will assist in
turning the eye upward.  Conversely, when the
eye is turned downward so that its equator lies
above the line of these muscles, their contraction
will assist in turning the eye downward.  When
the eye is turned outward so that its equator lies
inside the line of the superior and inferior recti,
their contraction would assist in turning the eye
outward.  When the eye is turned inward so that
the equator lies outside of the line of the superior
and inferior recti, their contraction would assist
in turning the eye inward.
  In taking into consideration the chief action of
any one or more muscles, the above associated
movements should always be understood and
considered.





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        | End of Chapter XII |  pages 171-173
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