380 THE MUSCULAR SYSTEM. 
The obliquus inferior arises from the inner side of the floor of the orbit just 
behind its anterior margin, and external to the naso-lachrymal groove. It forms 
a slender rounded slip, which curls round the inferior rectus tendon, and passes 
between the external rectus and the eyeball, to be inserted into the sclerotic 
between the superior and external recti, and further back than the superior 
oblique muscle. 
Miiller’s muscle is a rudimentary bundle of non-striated muscular fibres bridging across the 
Frontal nerve 
Lachrymal gland Supra-orbital nerve 
Lachrymal nerve-—— 
—Supra-trochlear nerve 
LEVATOR PALPEBRA 
SUPERIORIS 
Nerves to rectus superior and 
levator palpebree superioris,__ 
ae > - Or Tye . 
from oculo-motor nerve -__—_—+—— RECTUS SUPERIOR 
\ 
» 
—-- OBLIQUUS SUPERIOR 
= pT Nasal nerve — 
Sle 
= Infra-trochlear nerve 
<= CTUS INTERNUS 
—41___ Nerve to rectus internus from 
oculo-motor 
——— ay pe artery 
Optic nerve 
-— Long ciliary nerves 
Trochlear nerve 
RECTUS EXTERNUS 
Abducent nerve 
Oculo-motor nerve (inferior_ 
division) 
Lenticular ganglion— 
Nerve to rectus inferior, from_ 
oculo-motor nerve” Winn 
Nerve to obliquus inferior, — 
= — 
from oculo-motor nerve 
7 = Reerus INFERIOR 
OBLIQUUS INFERIOR 
Fira. 279.—ScHEMATIC REPRESENTATION OF THE NERVES WHICH TRAVERSE THE CAVITY OF THE ORBIT. 
spheno-maxillary fissure and infraorbital groove. It is supplied by fibres from the sympathetic, 
and may have a slight influence in the protrusion of the eyeball. 
NERVE SUPPLY. 
The muscles of the orbital cavity are supplied by the third, fourth, and sixth cranial nerves. 
The fourth nerve (trochlearis) supplies the obliquus superior; the sixth (abducens) supplies the 
rectus externus; the third nerve (motor oculi) supplies the others—levator palpebrée superioris, 
recti, superior, inferior and internus, and obliquus inferior. 
ACTIONS. 
The levator palpebre superioris elevates the upper eyelid and antagonises the orbicularis 
palpebrarum muscle. The six muscles inserted into the eyeball serve to move the longitudinal 
axis of the eyeball upwards, downwards, inwards, and outwards, besides causing a rotation of the 
eyeball on its own axis. The following table expresses the action of individual muscles. It must 
be remembered that, while similar movements occur simultaneously in the two eyeballs, the 
horizontal movements may, by adduction of the muscles of both sides, cause convergence of the 
axes of the two eyeballs for the purposes of near vision. 
a. Adduction and Abduction. 
Rectus externus 
Obliquus superior | (correcting 
Obliquus inferior J adductors) 
Rectus superior \ 
Rectus internus | 
Rectus interior { | 
| b. Elevation and Depression. 
Rectus superior 
Obliquus inferior | 
Rectus inferior 
Obliquus superior 
c. Rotation outwards. 
Rotation inwards. 
Obliquus inferior | 
Obliquus superior 
Rectus superior } : 
Rectus inferior p07” *@auctton) 
