788 
The malar branch passes on to the inferior 
external angle of the orbit, where it sometimes 
communicates with the lachrymal nerve; it 
enters one or more canals in the malar bone, 
and appears on the facial surface, supplying 
the orbicularis and the integuments, and com- 
municating with the portio dura. 
In addition to the structures ordinarily 
described as existing within the orbit, Mr. 
O’Ferrall has described * a fibrous structure, to 
which he gives the name of “ tunica vaginalis,” - 
and which invests the globe of the eye, one 
rating it from the muscles and fat of the orbit. 
In order to expose the outer surface of this 
Structure, a vertical incision must be made 
through the integument of the upper lid; after 
removing carefully the orbicularis and a fascia, 
between the two layers of which the tendon of 
the levator palpebre is inserted, the part 
next in order is the tarsal cartilage. Tracing 
this upwards and backwards its thin’margin is 
found to be continuous with a fibrous lamina, 
which passes back into the orbit and separates 
the globe of the eye from the superior rectus 
muscle, but presenting a well-defined opening, 
through which the tendon of the muscle passes 
as overa pulley, to be inserted into the scle- 
rotic coat. In order to examine the ocular sur- 
face of this membrane, Mr. O’Ferrall advises 
a vertical division of both palpebra, then an 
incision through the conjunctiva at the angle 
of reflection from the eyelid to the ball of the 
eye. ' 
The incision being made and the edges of 
the divided membrane separated, we expose 
the ocular surface of “a distinct tunic of a 
yellowish white colour and fibrous consistence, 
continuous in front with the posterior margin 
ofthe tarsal cartilage, and extending back- 
wards to the bottom or a ta of the orbit, where 
its consistence becomes less strongly marked.” 
This ocular surface is smooth where the eye 
glides over it in its movements, and is con- 
nected to the surface of the globe by fine cel- 
lular tissue. The muscular substance of the 
recti muscles is on the outside of this tunic 
and invisible through it; but about half an 
inch posterior to its anterior margin are six 
well-defined openings through which the ten- 
dons of the muscles emerge in passing to their 
insertion in the sclerotic coat. Mr. O’Fer- 
rall was induced to look for this structure in 
consequence of meeting with cases in which 
the globe of the eye and the conjunctiva were 
protruded in a manner not satisfactorily ex- 
plained by reference to any previously described 
structure. He believes these to have been cases 
of inflammation of this tunic, with effusion 
. between its deep surface and the globe of the 
eye. 
Mr. O’Ferrall believes that “the uses of 
this tunic are to present a smooth surface, faci- 
litating the movements of the eye; and by its 
density and tension, to protect it from the pres- 
sure incidental to the swelling of its muscles 
during their action. That the openings in this 
* Dublin Journal of Medical Science, July, 
ORBIT. 
tunic perform the office of pulleys, giving a 
proper direction to the fores exerted by the 
muscles,—securing the motions of rotation, and 
opposing those of retraction, which would other- 
wise predominate.” 
Action of the muscles.—The action of the 
levator palpebre muscle is to raise the 1 
lid, and thus to ex the anterior part of the 
eye-ball. In this action it is an associate of the 
frontal portion of the occipito-frontalis, and an— 
antagonist of the orbicularis palpebrarum. 
C. Bell* affirmed that the action of the levator 
palpebee is not simply that of raising the upper 
id, but that the swelling and tension of th * 
muscle during its pene the be 
ushing forwards the eye- us ing the 
Ga lid to slide off the convex oan + 
eye, and to be depressed whilst the upper lid 
is elevated. There is no proof of any such 
action of the levator palpebre, and it seems 
improbable that it should exert any such in- 
fluence, separated as it is from the 
the superior rectus, by a considerable quantity 
of fat and by the “ tunica vaginalis.” The re- 
sult of paralysis of this muscle is a dropping of 
the upper lid, to which the term ptosis is applied. 
It is evident from an examination of the 
origin, course, and insertion of the recti museles 
that each of them acting singly is capable of 
making the eye-ball revolve in its own direc 
tion; the superior rectus directs the cor 
upwards; the inferior rectus antagonises t 
superior and directs the cornea down 
the external rectus directs it outwards and i 
antagonised by the internal, which draws th 
cornea inwards towards the nose. It is 
evident that the action of any two contigu 
recti muscles will give the cornea a di 
intermediate between that which it would a 
sume from the action of each of them singly 
the superior and internal recti acting toget 
will direct ‘the cornea upwards and inwar 
while the inferior and external will direct 
downwards and outwards ; so that the con 
may be made to assume any intermediate 
tion by the action of the recti muscles alone. 
The successive action of all the recti mi 
cles would produce a movement of the ¢ 
ball analogous to circumduction of a li 
and as the circumduction of a limb is a m 
ment altogether distinct from rotation, st 
this circeumduction of the eye-ball entirely 
tinct from any rotation upon its antero-post 
axis. In cireumduction the centre of 
cornea describes a circle, whereas in ro 
this point remains fixed, forming the a 
extremity of an imaginary axis, round 1 
the circumference of the cornea revolve! 
is of much importance to have a di 
notion of each of these movements, as wi 
thus avoid one source of confusion in 
sidering the action of the straight and ¢ 
muscles of the eye. Having thus ¢ 
rotation, no argument is necessary to pro 
the recti muscles are incapable of pros 
such a movement; a glance at their dire 
2 
recih 
4 
* The Nervous System of the Human Bos 
Sir C, Bell. a 
