ORBIT. 
the third, and the optic nerves, with the 
ophthalmic artery and the eye-ball. 
The vbliquus superior is a long and slender 
muscle, which is sometimes called the trochlearis 
muscle from the fact of it being reflected through 
a trochlea or pulley. It arises from the fibrous 
sheath of the optic nerve, and from the inner 
part of the optic foramen between the superior 
and internal recti muscles ; it passes forwards 
along the internal superior angle of the orbit, in 
the form of a rounded fleshy belly, to which 
succeeds a rounded tendon, which after passing 
through the pulley beneath the internal angular 
process is directed backwards, outwards, and 
downwards, passing beneath the superior rectus 
' muscle to be inserted by a thin aponeurosis into’ 
the sclerotic coat between the superior and exter- 
nal rectus, rather behind the anterior half of the 
_ globe. This pulley or trochlea, through which 
»passes the tendon of the superior oblique, is a 
_ small cartiliginous ring, inserted by means of 
fibrous tissue into a depression beneath the 
internal angular process ; it is lined by a syno- 
vial membrane. The orbital surface of the 
superior oblique is in contact with the perios- 
| teum; the fourth nerve passes into this surface 
_ about its centre; the relations of its ocular 
_ surface are the same as those of the superior 
rectus. 
_ The superior rectus and superior oblique 
| Mouscles may now be cut through and turned 
_ aside, and after removing carefully some fat 
_and cellular tissue the following parts are 
brought into view :—the internal and external 
_ recti muscles, the optic, the third, and the nasal 
_ branch of the ophthalmic nerves, the lenticular 
ganglion between the optic nerve and external 
rectus muscle, and the ophthalmic artery and 
vein. 
| The third nerve before entering the orbit 
divides into two portions; a superior smaller, 
and an inferior larger ; it enters the orbit through 
_ the sphenoidal fissure between the two heads of 
the external rectus muscle ; the inferior division 
t er om beneath the globe of the eye and 
‘must be examined in a subsequent stage of the 
‘dissection. The superior division is now visible; 
it passes to the under surface of the superior 
Tectus muscle, to which it sends numerous fila- 
‘Ments; some filaments also pass on the inner 
ide of the superior rectus and enter the deep 
‘surface of the levator palpebre superioris ; these 
are the only muscles supplied by this division 
(of the third nerve. 
i The nasal nerve is in size the second branch 
of the first division of the fifth. It enters the 
orbit through the sphenoidal fissure, passing 
between the two heads of the external rectus 
nuscle, in company with the third and sixth 
lerves, being external to the former, and be- 
yeen its two divisions, and internal and some- 
what superior to the latter. Having entered the 
Orbit, it passes forwards and inwards towards the 
hternal wall, crossing over the optic nerve 
between it and the superior rectus muscle; it 
las also above it the levator palpebr and supe- 
jior oblique muscles, and the superior division 
bf the third nerve; it passes out of the orbit 
jhrough the anterior internal orbital hole in 
} VoL. 111. 
785 
company with the anterior ethmoidal artery. 
Within the orbit it sends off lenticular, ciliary, 
and infra-trochlear branches. The lenticular 
branch is given off on the outer side of the optic 
nerve ; it anastomoses with the superior division 
of the third nerve, and joins the posterior supe- 
rior angle of the lenticular ganglion. The 
ciliary branches are two or three in number ; 
given off above the optic nerve, they pass for- 
wards and pierce the posters part of the 
sclerotic. The infra-trochlear branch is given 
off near the inner wall of the orbit ; it passes out 
beneath the pulley of the superior oblique 
muscle, and sends branches to the superior eye- 
lid, the lachrymal sac, and integuments of the 
nose; within the orbit there is an anastomosis be- 
tween thisand thesupra-trochlearor frontal nerve. 
The denticuldr or ciliary ganglion is situated 
in the posterior and outer part of the orbit 
between the optic nerve and the external rectus 
muscle; it is very small, and of a somewhat 
square form. Its superior posterior angle is 
joined by.the lenticular branch of the nasal nerve, 
which constitutes the long root of the ganglion ; 
its inferior posterior angle receives a branch 
from the inferior division of the third nerve ; this 
forms the short root of the ganglion. To its 
posterior part is also connected one filament 
from the cavernous plexus, and occasionally 
one from, the spheno-palatine ganglion. From 
the anterior part of the ganglion a number of 
delicate ciliary nerves pass off; they are divided 
into two sets, one set coming from the superior 
anterior, and the other from the inferior anterior 
angle of the ganglion ; the former are the more 
numerous; in all they are from twelve to sixteen 
in number; they pass forwards and pierce the 
sclerotic near the optic nerve. 
The optic nerve passes forwards from the 
optic hole to the inner and back part of the 
eyeball, which it enters to terniinate in the re- 
tina. It is invested by a sheath of fibrous 
membrane, which is continuous behind with the 
dura mater, and in front with the sclerotic ; the 
outer surface of this sheath posteriorly gives 
attachment to the recti muscles, which surround 
the optic nerve ast emerges from the optic 
hole. The optic nerve is crossed above by the’ 
nasal nerve and the ophthalmic artery, below by 
the branch of the inferior division of the third 
nerve, which supplies the internal rectus muscle ; 
it is surrounded by numerous delicate ciliary 
nerves aud arteries. 
The ophthalmic artery passes through the 
optic hole in company with the optic nerve, 
and inclosed in a sheath derived from the dura 
mater. It is very tortuous and twines round 
the optic ‘nerve, being at first inferior to the 
nerve, then passing to its outer side, and soon 
crossing over it to reach its inner side; it then 
passes across to the inner wall of the orbit, 
where it breaks up into its terminal branches. 
The branches of the ophthalmic artery are very 
numerous ; they may be arranged in three sets ; 
the first set arises from the artery as it lies ex- 
ternal to the optic nerve; it consists of the 
lachrymal and the centralis retine ; the second 
set comes off from the artery, when it 1s above 
the optic nerve; this consists of the supra- 
3 E 
