636 THE NERVOUS SYSTEM. 
receives a slender communication from the ophthalmic division of the fifth nerve. 3. The @ 
short root of the ciliary ganglion passes upwards from the branch of the nerve which 
supplies the inferior oblique muscle. | 
THE FourtH or TROCHLEAR NERVE. 
surface of the mid-brain. It springs at the side of the frenulum from the 
_ Intra-trochlear nerve 
Olfactory bulb Wa Supra-trochlear nerve 
x 
- A nerve 
_Spheno-parietal sinus 
Optie nerve 
4 
¥ 
: 
The trochlear nerve (n. trochlearis or patheticus) emerges from the dorsal 
_~ Ophthalmic vein 
_ Anterior clinoid 
Optic commissure y) \ —"_ process . 
Anterior cerebral : _-— Trochlear nerve | 
artery iN 
i \ Oculo- 
Middle cerebral | a culo motor 
artery | : nerve 
Posterior 
communi- 
cating artery 
Oculo-motor-~ 
nerve 
Posterior cere- — 
bral artery 
Superior cere- 
bellar artery 
Trochlear 
nerve 
Abducent nerve 
— Circular sinus 
-~ Ophthal. nerve 
Superior 
maxillary nerve 
Inferior 
maxillary nerve 
Cavernous sinus 
~ Basilar sinus | 
__ Gasserian — 
Abducent ganglion 
nerve __ Basilar 
| artery 
2 | ! S\N Inferior 
ieee WAN Se : F \: \° . . \ vat! 
Prigeminal He Hf { ‘ \ —petrosal 
nerve | 
: sinus 
Superior fj 
petrosal ; Vertebral — 
sinus al | y artery 
Facial ) Bi 
nerve \ 
Sigmoid 
sinus 
J 
{ 
; 
Pars inter- 4 \o 
media \\ 
Auditory nerve % \3A 
Way 
\\ 
Glosso-pharyn- .\ / 
geal nerve .\ 
Pnenumogastric 
nerve 
Spinal accessory nerve 
Lateral sinus 
Tentorium cerebelli 
(cut) 
’ ~Occipital sinuses 
Hypoglossal nerve 
Lateral Sinus 
<< 
Vertebral artery es oe L 
Straight sinus 
Spinal cord Toreular Herophili 
J 
“, 
Openings of occipital sinuses% Superior longitudinal sinus 
Falx cerebri (eut) 
Fig. 457.—THE Base oF THE SKULL. to show the dura mater, sinuses, arteries, and nerves. 
anterior end of the superior medullary velum, just behind the corpora quadri- 
gemina (for deep origin, see p. 499). It is extremely slender, and of consider- 
able length. Passing round the crus cerebri, the nerve appears in the base of 
the brain behind the optic tract, in the interval between the crus cerebri internally 
and the temporal lobe of the cerebrum externally. Continued forwards to the base 
of the skull, it pierces the free border of the tentorium cerebelli, on the outer side 
of the third nerve, and proceeds forwards in the outer wall of the cavernous sinus 
lying between the third and ophthalmic nerves. It enters the orbit through the 
