Bauhaus-Universität Weimar

THE MOTOR NERVES. 
593 
contracted for an instant on each injury of the nerves. A pheno¬ 
menon observed by Flourens also. 
* 5. When the third nerves are irritated in the living or dead bird, 
a like result ensues. 
6. When the fifth nerve is similarly irritated in the dead bird, no 
affection of the pupil is observed. 
7. When the optic nerves have been divided within the cranial 
cavity of a pigeon immediately after its decapitation, if the portion 
of the nerves attached to the eyes be pinched, no contraction of the 
pupil ensues: if the portion adhering to the brain be pinched, a like 
contraction of the pupil ensues, as if the optic nerves had not been 
divided. 
8. The previous division of the fifth nerves in the preceding ex¬ 
periment produces no difference in the result. 
9. When the third nerves have been divided in the cranial cavity 
of the living or dead bird, no change in the pupil ensues on irritating 
the entire or divided optic nerves. (Mayo's Anat. and Physiol. 
Commentaries, 1823, pt. ii. p. 4.) 
From these experiments we may with confidence conclude that the 
motor power of the ciliary ganglion and the ciliary nerve is derived 
from the third nerve, and that the light does not cause the contrac¬ 
tion of the pupil by acting directly upon the ciliary nerves: but that 
the irritation of the retina and optic nerve acts immediately upon the 
brain, and from the brain is reflected upon the third nerve and the 
short motor root of the ciliary ganglion. 
Hence we have voluntary power over the motions of the iris; in 
other words, whenever the third nerve is excited to action by voli¬ 
tion, the iris contracts. Now, in looking at near objects, the axes of 
the eyes are made to converge,—the eyes are turned inwards; and 
hence, when we direct our eyes to near objects, the pupil becomes 
much contracted, but dilates when we look at distant objects. The 
pupil becomes very narrow in birds when we approach them, and 
they become agitated; but the motions of the iris are not really more 
subject to the will in them than in man. 
It is not, however, the branch of the third which goes to the in¬ 
ternal rectus muscle only that has this sympathetic influence over the 
iris; other branches, more especially that which supplies the inferior 
oblique muscle, have the same power. The inferior oblique muscle 
rotates the eye so*as to carry the pupil upwards and inwards: if this 
movement is expcuted voluntarily, the pupil becomes much con¬ 
tracted. The eye takes this position involuntarily when sleep is 
coming on, in sleep itself, in the state of intoxication, and in hysterical 
attacks; hence we find the pupil contracted during sleep. 
The contracted pupil of sleep can, however, be made to contract 
still more, according to the observation of Mr. Hawkins, (Mayo's 
Commentaries, pt. ii. p. 6,) by the admission of intense light. At the 
moment of waking, the pupil, after a few irregular contractions, as¬ 
sumes its usual degree of dilatation. 
The third nerve seems to determine only that movement of the 
iris which produces contraction of the pupil. There are many cir- 
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