784 
noidal fissure. Entering the optic hole it 
divides into two portions, one forming a tu- 
bular sheath for the optic nerve, and becoming 
continuous with the sclerotica, the other form- 
ing the proper periosteum. Where it enters 
the sphenoidal fissure it also forms a sheath for 
the vessels and nerves which pass through that 
opening. At the anterior margin of the orbit 
this fibrous membrane divides into two por- 
_ tions, one becoming continuous with the pal- 
pebral ligament or fascia, the other with the 
periosteum of the forehead. 
The periosteum may now be removed, and 
the following parts are seen immediately be- 
neath it: in the middle line the frontal branch 
_ of the ophthalmic division of the fifth nerve, 
on the outer side the lachrymal branch of the 
same nerve, and on the inner side is the fourth 
nerve. Immediately under the fourth nerve is 
the superior oblique muscle; beneath the fron- 
tal nerve are the levator palpebre and superior 
rectus, and below the lachrymal nerve is the 
external rectus muscle; beneath the external 
angular process is the lachrymal gland. Some 
branches of the ophthalmic artery are seen in 
this part of the orbit. A considerable quantity 
of soft fat exists in the orbit, filling up the 
intervals between the muscles and other parts ; 
some of this must be removed before a clear 
view can be obtained of the parts which we 
have enumerated as being visible in this stage 
of the dissection. 
The lachrymal gland is contained in a de- 
pression on the roof of the orbit, beneath the 
external angular process of the frontal bone. It 
is generally about as large as a filbert, of an 
irregular ovoid form, with its long diameter 
placed transversely. Its upper surface is con- 
vex, and connected by means of fibrous pro- 
cesses to the periosteum; its under surface is 
concave, and is in relation with the external 
rectus muscle and the eye-ball. The excretory 
ducts of this gland, from ten to twelve in num- 
ber, run parallel to each other, and open by as 
many orifices beneath the upper lid, about a 
line from the tarsal cartilage. 
The fourth nerve enters the orbit by passing 
through the inner part of the sphenoidal fissure. 
At this point it is above the other nerves, which 
pass through the same opening. It then passes 
forwards and inwards immediately under the 
periosteum, crossing over the origin of the leva- 
tor palpebre and superior rectus muscles, and 
it is distributed to the orbital surface of the 
superior oblique muscle. 
e frontal nerve,a branch of the ophthalmic 
division of the fifth, enters the orbit with the 
fourth nerve, but a little below it and on its 
outer side. It passes forwards between the 
periosteum and the levator palpebre, and soon 
divides into two branches, internal and external 
frontal, or supra-trochlear, and supra-orbital. 
The supra-orbital is the larger branch ; it passes 
out through the supra-orbital notch or foramen, 
and divides into ascending frontal branches, 
usually two in number, which are distributed to 
the skin of the forehead, and descending palpe- 
bral filaments, which are very numerous and are 
distributed in the substance of the upper eyelid. 
ORBIT. 
The supra-trochlear nerve passes out of the 
orbit between the supra-orbital notch and the © 
pulley of the superior oblique; it gives off — 
ascending frontal filaments to the skin of the ; 
forehead, and descending palpebral and nasal 
filaments to the upper eyelids and dorsum of the — 
nose, “a 
The lachrymal nerve is the smallest of the 
three divisions of the ophthalmic; it enters the 
orbit through the sphenoidal fissure external 
and inferior to the frontal nerve ; in its pa: 
through the sphenoidal fissure it is invested in 
a sheath of dura mater. It runs along the si 
perior border of the external rectus muscle, 
immediately under the periosteum; it passes 
through the lachrymal gland, sending numerous: 
filaments to it, and terminates by sending 7 
pebral filaments to the upper isd, ene of 
passes on and is distributed to the skin of the 
anterior temporal region. In its course it gives 
off a malar branch, which passes through a 
canal in the malar bone and is distributed to 
the skin on the cheek ; it also sends down c 
or two filaments which anastomose with # 
superior maxillary branch of the fifth nerve.* — 
e may now examine the three muse! 
which are placed most superficially in the uppe 
part of the orbit, and which are visible in th 
stage of the dissection, viz. the levator palpebr: 
a espe rectus, and the superior oblique. 
e levator palpebre supertoris arises té 
dinous from the inferior surface of the less 
wing of the sphenoid bone above the op 
foramen, also from the fibrous sheath of t 
optic nerve; it passes forwards, and upwar 
becoming broader and thinner towards the a 
terior part of the orbit, where it suddenly curt 
downwards and ends in a broad thin a 
neurosis, which is inserted into the upper 
der of the tarsal cartilage, behind the palpe 
ligament. This muscle is of a triangular fo 
the apex being posterior; it is crossed by 
fourth and frontal nerves, the latter passing | 
ward above and parallel to it, and separatin 
from the periosteum; it covers the 
rectus and eyeball. 
In order to expose the superior rectt 
through and turn aside the levator palpet 
doing so a small branch of the third ne 
seen to enter its inferior surface. 
The rectus superior arises from the v 
part of the fibrous sheath of the optic nerve 
from the outer and upper part of the m 
the optic foramen ; the fleshy fibres frot 
point of origin pass forwards and outwal 
the direction of the axis of the orbit; the: 
becomes broader and thinner anterior 
ends in a broad aponeurotic expansion, 
is inserted into the upper aspect of the s 
a little behind the margin of the corné 
small synovial bursa is said to exist betw 
sclerotic and the tendon at its insertion 
muscle is covered above by the leva 
pebre, and by the nerves which cross the 
palpebre ; below it is in relation with the 
* For a more minute account of the dis 
of these branches of the fifth nerve, see 
Fiera NERVE, . a 
