ORBIT. 
backwards in the same direction as the artery, 
but it is much less tortuous. It receives 
branches corresponding to those which the 
artery gives off, and passing between the two 
heads of the external rectus muscle below the 
nerves, it terminates in the anterior extremity 
of the cavernous sinus. 
The ophthalmic artery and vein may now be 
removed; cut through the optic and ciliary 
nerves and remove some fat and cellular tissue 
which obscures the remaining muscles and 
nerves ; we now obtaina more clear view of the 
internal and external recti muscles, and at the 
same time we expose the sixth nerve and the 
inferior division of the third, as well as the 
inferior rectus and the inferior oblique muscles. 
_ The siath nerve passes between the two 
heads of the external rectus muscle below the 
_ third nerve, and above the ophthalmic vein, 
_ from which it is separated by a process of dura 
mater. Having entered the orbit it passes along 
the inner surface of the external rectus muscle, 
_ to which it is distributed by numerous delicate 
- filaments. 
_ The inferior division of the third nerve 
enters the orbit, as we have seen, between the 
_ two heads of the rectus muscle, where it lies a 
little above the sixth nerve ; having entered the 
‘orbit it passes down towards the floor between 
the optic and the sixth nerves, and below the 
level of the latter. It almost immediately di- 
vides into three branches: an internal, which 
passes inwards beneath the optic nerve towards 
the internal rectus muscle, to the ocular surface 
‘of which it is distributed ; a middle branch, 
which is distributed in the same manner to the 
ocular surface of the inferior rectus; and an 
vternal, which passes forwards along the ex- 
ternal border of the inferior rectus, and enters 
the posterior border of the inferior oblique, 
almost at right angles. The short filament 
hich joins the posterior inferior angle of the 
enticular ganglion, forming the short root of 
‘the ganglion, is usually given off from the 
branch which goes to the inferior oblique 
_ muscle. ; 
The external rectus muscle has two origins, 
2 from a tendon, the tendon or ligament of 
inn, which is common to this muscle with 
he inferior and internal recti, and which is 
‘attached to a little tubercle behind the optic 
‘foramen; the other origin of the external rectus 
ts above, from the inner margin of the sphe- 
noidal fissure ; this origin is united with the 
origin of the superior rectus. Between these 
‘two origins pass the third, the sixth, and the 
asal branch of the fifth nerves, with the oph- 
‘thalmic vem. From its origin the external 
us passes forwards along the external wall 
the orbit; it turns over the globe of the eye, 
d is inserted by a thin tendinous expan- 
ion just behind the margin of the cornea. A 
small bursa intervenes between the tendon and 
the sclerotic, as is the case with the tendons of 
| the recti muscles. 
_ The internal rectus arises from the common 
lendon or ligament of Zinn, and from the 
ibrous sheath of the optic nerve; it passes 
iorwards along the internal wall of the orbit, 
787 
turns over the globe\of the eye, and is inserted 
immediately oppositethe external rectus, in 
the same manner as the other recti muscles. 
* The inferior rectus muscle arises from the 
common tendon, between the internal and ex- 
ternal recti; it passes forwards under the globe 
of the eye and is inserted into the sclerotic in 
the same manner as the preceding muscles, 
and immediately opposite the superior rectus. 
The recti muscles have all the same form, viz. 
that of a long isosceles triangle, having the base 
directed forwards, and the apex backwards. 
They differ in length and thickness; the in- 
ternal rectus being the shortest and thickest, 
the external rectus the longest, and the superior 
rectus the smallest.* 
The inferior oblique muscle is the only one 
which does not arise from the apex of the orbit. 
It arises from the orbital plate of the superior 
maxillary bone, just within the margin of the 
orbit, and near the groove for the lachrymal sac. 
From its origin it passes obliquely outwards, 
upwards, and backwards beneath the globe of 
the eye and the inferior rectus, thén between 
the former and the external rectus; it ends in 
an aponeurotic expansion which is inserted 
into the sclerotic between the superior and ex- 
ternal recti, opposite the insertion of the su- 
perior oblique, and rather nearer the optic 
nerve than the insertion of that muscle. The 
superior surface of this muscle is in contact 
with the inferior rectus and the globe of the 
eye; the inferior touches the floor of the orbit 
and the external rectus muscle; its borders are 
anterior and posterior ; a branch of the third 
nerve enters the posterior border. ' 
The orbital portion of the superior maxillary 
nerve may now be exposed by cutting through 
the external rectus muscle, and drawing the 
eye with its muscles towards the inner part of 
the orbit. The nerve having crossed the spheno- 
maxillary fossa enters the orbit through the 
spheno-maxillary fissure; in company with a 
branch of the internal maxillary artery it passes 
along the jnfra-orbital groove, covered by a 
layer of periosteums it then passes through the 
canal and emerges from the infra-orbital fora~ 
men. The trunk of the nerve is but little vi- 
sible on the floor of the orbit. While the supe- 
rior maxillary nerve is in the foramen rotun- 
dum, or during its passage across the fossa, it 
sends off a temporo-malar branch which passes 
through the spheno-maxillary fissure superior 
and external to the trunk of the nerve; it passes 
along the floor of the orbit, beneath the inferior 
rectus muscle, and about the middle divides 
into two branches, a temporal and a malar. 
The temporal branch goes towards the outer 
wall of the orbit, passes up between the bone 
and the external rectus muscle, and joins with 
a temporal branch from the lachrymal ; it then 
pierces the orbital process of the malar bone 
and enters the temporal fossa, where it com- 
municates with the anterior deep temporal 
nerve, sends branches to the temporal muscle, 
and piercing the fascia is distributed to the 
skin over the temporal region. 
* Cruveilhier. Descriptive Anatomy, 
3 E2 
‘ 
