THE THIRD OR OCULO-MOTOR NERVE. 635 
is crossed by the ophthalmic artery and the nasal nerve, and nearer to its 
termination it is surrounded by the ciliary vessels and nerves, and by the capsule 
of Tenon. It is pierced obliquely on its under surface by the central artery of 
the retina. 
Decussation in the Optic Commissure.—In the optic commissure the fibres of the two 
optic tracts separate, the inner half of each tract decussating to form the mesial half of the opposite 
optic nerve. The other, outer half of each tract continues its course to form the outer half of 
the optic nerve on the same side. At the back of the commissure another bundle of fibres is 
found passing from tract to tract behind the decussating fibres, and known as G@udden’s commis- 
sure (see p. 510). 
THE THIRD OR OCULO-MOTOR NERVE. 
The oculo-motor nerve (n. oculo-motorius) arises from the brain, in the 
region of the posterior perforated spot, by several radicles emerging trom the 
Internal carotid artery Optic nerve _ 
Trochlear nerve | Ophthalmic artery 
Oculo-motor nerve | / Anterior clinoid process 
Diaphragma sellie | as | Trochlear nerve 
: Frontal branch 
Lachrymal branch 
Oculo-motor nerve 
(superior division) 
27 Nasal branch of ophthalmic 
Z nerve Z 
g Oculo-notor nerve 
= (interior division) 
Abducent nerve 
Superior maxillary division of 
z Gy trigeminal nerve 
Sphenoid bone——>-— 5 
= 
Internal carotid artery aN 
| Foramen ovale 
| Inferior maxillary division of trigeminal nerve 
Motor root 
Cavernous sinus 
Ophthalmic division of trigeminal nerve; ( 
Superior maxillary division of trigeminal nerve | 
Inferior maxillary division of trigeminal nerve 
Fig. 455.—RiELATIONS OF STRUCTURES IN THE CAVERNOUS SINUS AND SPHENOIDAL FISSURE. 
oculo-motor sulcus, on the inner side of the crus cerebri, just in front of the pons 
Varolu (Fig. 452). Passing forwards between the posterior cerebral and superior 
cerebellar arteries, the nerve pierces the dura mater on the outer side of the 
posterior clinoid process, in a small triangular space between the free and attached 
borders of the tentorium cerebelli. Beneath the dura mater the nerve courses 
through the outer wall of the cavernous sinus, and enters the orbit through the 
sphenoidal fissure and 
between the two heads of Posterior _ 
the external rectus muscle. 7" [> 
As it enters the orbit it 
divides into upper and 
lower branches, separated 
by the nasal nerve. 
Brane hes. — hve Ce, 
superior branch of the quadrigemina ~ 
nerve supplies two muscles 
of the orbit—the superior 
rectus and the levator 
palpebree superioris. 
The inferior branch Frenplum veli 
> Superior medullary veluim 
passes forwards, and after - 
giving branches to the [!6¢- 456.-—DorsaL SURFACE OF THE Mrp Brain, to show the origin 
2 of the trochlear (fourth) nerve. 
ineal body 
Pineal body Optic thalamus 
-Brachia conjunctiva 
_— Fourth nerve 
—_—§Fillet 
Superior peduwicle of 
; cerebelluin 
~~ Crus cerebri 
— Lingula 
internal and inferior recti, 
ends in the inferior oblique muscle. The short root of the cilary ganghon arises 
from the terminal branch to the last-named muscle. 
Communications._-1. In the cavernous sinus the third nerve communicates with 
the cavernous plexus on the internal carotid artery. 2. In the cavernous sinus it also 
