ORBIT. 
and their position with regard to the eye-ball 
will at once deterinine this point. If then any 
such movement occurs, other muscles must be 
provided in order to effect it. 
We now proceed to consider the action of 
the oblique muscles. 
It may be well to remind the reader that, in 
all the vertebrate animals, these muscles have 
essentially the same direction and relations ; 
the only difference being that in fishes, rep- 
tiles, and birds, the superior oblique arises 
from the anterior part of the orbit, whence it 
passes backwards and outwards to its insertion ; 
whereas, in Mammalia, it comes from the pos- 
terior part of the orbit and passes through a 
tendinous pulley before taking its course back- 
_ wards and outwards ; the action of the muscle 
will obviously be the same in both cases. One 
function which has been assigned to the oblique 
muscles, is that of antagonising the recti so as 
to prevent the retraction of the eye-ball within 
_ the orbit during the action of the latter mus- 
cles. To this conclusion Sir C. Bell asserts 
there are many objections: two of these ob- 
jections we subjoin in his own words. “4. 
In creatures where the eye is socketed in a 
cup of cartilage and cannot retract, the oblique 
muscles are nevertheless present. 2. Where a 
‘powerful retractor muscle is bestowed in ad- 
dition to the recti muscles to pull the eye-ball 
back, the oblique muscles have no additional 
Magnitude given to them to pull the eye-ball 
forwards.” Now we must not suppose that the 
gonism exerted by the oblique muscles is 
“such as to oppose the conjoint forcible action, 
| or active contraction, of all the recti muscles, 
d of a retractor when such a muscle exists. 
| If such were the case, we should certainly find 
‘the developement of the oblique muscles in 
Some degree proportioned to that of the mus- 
‘tles they were intended to antagonise, and a 
cup of cartilage at the back of the eye-ball 
Would apparently supersede the necessity for 
‘ny antagonism on the part of the oblique 
' 
" 
; 
e oblique muscles probably exert upon the 
fecti is equally necessary whether the eye-ball 
be encased in cartilage or supplied with a re- 
tractor muscle. It is simply the same kind 
antagonism which the muscles on the op- 
Osite sides of the face exert upon each other. 
paralysis of the pertio dura on one side is 
uttended with a traction of the features to the 
Opposite side; this results from the ordinary 
lonicity or passive contraction of the muscles 
m the one side, unopposed by the correspond- 
§ force on the other; the distortion is gene- 
‘ally conspicuous enough when the muscles are 
test, but when they are thrown into active 
Ontraction it becomes still more marked, 
md the movements of the sound side are un- 
teady and oscillating. During the healthy 
ate then the symmetry of the features is 
naintained by this antagonism of the muscles 
nh opposite sides of the face. In like manner 
hen the muscles are at rest, the eye-ball is 
ept delicately balanced between its six mus- 
es; the superior rectus opposes the inferior, 
d the external opposes the internal, while 
muscles; but the kind of antagonism which 
789 
the obliqui are opposed to each other, and 
the recti conjointly are_antagonised in their 
retracting tendency by the opposite force of the 
obliqui. This is the condition during a state 
of rest, when the contraction of all the mus- 
cles is merely that of their ordinary tonicity or 
passive contraction. Now, suppose one straight 
muscle to be thrown into a state of voluntary 
"active contraction; immediately the cornea is 
directed towards that muscle, the antagonism 
of the other five muscles serving the important 
purpose of preventing any irregular oscillatory , 
movement of the eye-ball; when the contrac- 
tion of that muscle ceases, the eye is at once 
restored to its original position. One of the 
uses of the oblique muscles then is by their 
antagonism of the recti to assist in preventing 
any unsteady motion of the eye-ball. This, 
however, is by no means the only or the chief 
use of the oblique muscles, and the question 
arises, what movements of the eye-hall are 
effected by the contraction of these muscles? 
Upon this subject the most contradictory state- 
ments have been made; on the one hand 
Scemmering, Cloquet, and Harrison assert, that 
the superior oblique directs the pupil down- 
wards and inwards, the inferior oblique moves 
it upwards and outwards; on the other hand, 
according to Miiller, Monro, and Sir C. Bell, 
the superior oblique directs the pupil down- 
wards and outwards, the inferior oblique up- 
wards and inwards. All these anatomists 
agree in supposing that the oblique muscles 
effect what we have called circumduction of 
the eye-ball, but their disagreement as to the 
direction in which circumduction occurs under 
the influence of these muscles, is of itself an 
argument against the probability of any such 
movement being produced by them. We have 
before stated that the recti muscles are of them- _ 
selves capable of circumducting the eye in all 
directions; this was admitted and proved ex- 
perimentally by Sir C. Bell. He “ cut across 
the tendon of the superior oblique muscle of 
the right eye!of a monkey. He was very little 
disturbed by this experiment, and turned 
round his eyes with his characteristic inquiring - 
looks, as if nothing had happened to affect the 
eye.” In another experiment he “ divided the 
lower oblique muscle of the eye of a monkey. 
The eye was not, in any sensible manner, af- 
fected; the voluntary motions were perfect 
after the operation.” The result of these ex- 
periments appeared to Sir C. Bell to confirm 
the opinion which he entertained that the 
oblique muscles perform certain involuntary 
movements, such as the forcible elevation of 
the cornea under the upper lid when the eye 
is irritated, and the rolling of the cornea under 
the lid when tne eye is closed. He appears 
anxious to prove that the fourth nerve presides 
over the upward movement of the eye-ball 
which he says occurs during sneezing and 
certain other respiratory movements ; but as he 
has previously stated that the superior oblique 
to which the fourth nerve is distributed turns 
the eye downwards and outwards, in order to 
reconcile the two views he says, “ if we sup- 
pose that the influence of the fourth nerve is, 
