THE FASCIA AND MUSCLES OF THE ORBIT. 379 
The muscles of the orbit are seven in number: one, the levator palpebrie 
superioris, belongs to the upper eyelid; the other six are muscles of the eyeball. 
The levator palpebre superioris lies immediately beneath the orbital perios- 
teum over the superior rectus muscle. It has a narrow origin above that muscle 
from the margin of the optic foramen. em Lite etn A AP 
It expands as it passes forwards, to end, = | 
in relation to the upper lid, in a mem- 
branous expansion which 1s inserted in a 
four-fold manner: (1) slightly into the 
orbicularis palpebrarum and skin of the 
upper lid, (2) mainly into the upper 
border of the tarsal cartilage, (3) slightly 9. owes 
into the conjunctiva, and (4) by its edges svprrior® 
into the upper border of the margin of 
the orbital opening. 
The recti muscles are four in number 
—superior, inferior, internal, and external. 
They all arise from a membranous ring _ Recrvs 
surrounding the optic foramen, which is “""*"* 
separable into two parts—a superior com- 
mon tendon, giving origin to the superior 
and internal recti and the upper head 
of the external rectus; and an inferior 
common tendon, giving origin to internal 
and inferior recti and the lower head of 
the external rectus. The two origins of 
the external rectus muscle are separated 
by the passage into the orbit of the 
oculo-motor, nasal, and abducent nerves. Fig. 2/7.—THe Muscles oF THE ORBIT 
> : : (from above), 
Forming flattened bands which traverse 
the fat of the orbit around the optic nerve and eyeball, the four muscles end in 
tendons which pierce the capsule of Tenon, and are inserted into the sclerotic 
about eight millimetres (three to four lines) behind the margin of the cornea. 
The superior and inferior recti are inserted in the vertical plane slightly internal 
to the axis of the 
eyeball; the exter- 
nal and internal 
recti in the trans- 
verse plane of the 
RECTUS EXTERNUS eyeball ; and all 
Oculo-motor are attached in 
aie front of the 
equator of the 
eyeball. 
The obliquus 
Nasal nerve superior arises 
Abdueent nerve from the margin 
of the optic fora- 
men between the 
recti superior and 
OBLIQUUS INFERIOR REcrus INFERIOR 1 n t ernus. It 
passes forwards as 
anarrow muscular 
band internal to the rectus superior, and at the anterior margin of the orbit forms 
a narrow tendon which passes through a special fibrous pulley (trochlea) attached 
to the roof of the orbit. Its direction is thus altered, and passing outwards 
between the tendon of the superior rectus and the eyeball, it is inserted into the 
sclerotic between the superior and external recti, midway between the cornea and 
the entrance of the optic nerve. 
EXTERNUS 
\ 
RECTUS 
SUPERIOR 
LEVATOR PALPEBRA 
SUPERIORIS 
OBLIQUUS SUPERIOR 
LEVATOR PALPEBR& SUPERIORIS (cut) 
RECTUS SUPERIOR 
Fia, 278.—THE MUSCLES OF THE ORBIT (from without). 
