LATERAL PART OF MIDDLE CRANIAL FOSSA 239 



lateral wall of the cavernous sinus, and ends, close to the 

 superior orbital fissure, by dividing into three terminal branches. 

 As it traverses the sinus it is accompanied by the oculo- 

 motor and trochlear nerves, both of which occupy a higher 

 level. Like the other two divisions of the trigeminal nerve, 

 the ophthalmic nerve gives off a meningeal branch ; it is a 

 small twig which passes into the tentorium cerebelli. 



The terminal branches of the ophthalmic division of the 

 trigeminal nerve are the naso-ciliary, the lacrimal, and the 

 frontal. The naso-ciliary, as a rule, takes origin first ; 

 the lacrimal is given off soon after; and then the stem of 

 the nerve is continued onwards as the frontal. The three 

 branches enter the orbit through the superior orbital fissure. 



Nervus Oculomotorius (Third), et Nervus Trochlearis 

 (Fourth), et Nervus Abducens (Sixth). It has been noted 

 already that the oculo-motor nerve pierces the dura mater within 

 the small triangular area, in the middle cranial fossa, which 

 lies immediately anterior to the crossing of the attached and 

 free margins of the tentorium (p. 108). It has been noted 

 also that the trochlear (fourth) nerve pierces the dura mater 

 in the posterior fossa under the free margin of the tentorium. 

 Both proceed forwards in the lateral wall of the cavernous 

 sinus. The oculo-motor nerve occupies the highest level, 

 then comes the trochlear nerve, and immediately below that 

 the ophthalmic division of the trigeminal nerve. The three 

 nerves, therefore, present a numerical order from above down- 

 wards. The abducent nerve, which pierces the dura mater 

 in the posterior fossa, at the lower and lateral part of the 

 dorsum sellae, curves round the lateral side of the internal 

 carotid artery, and then passes forwards more directly within 

 the cavernous sinus than the others (Fig. 85). 



The oculo-motor, trochlear, and abducent nerves, during 

 their course *n the cavernous sinus, receive communica- 

 tions from the carotid plexus and from the ophthalmic 

 nerve ; and they all enter the orbit by passing through 

 the superior orbital fissure. Before doing so, the oculo- 

 motor nerve divides into an upper and a lower division. 

 As they pass through the superior orbital fissure the various 

 nerves undergo a change in their relative positions. That, 

 however, will be studied in the dissection of the orbit. 



Arteria Carotis Interna. The intracranial portion of the 

 internal carotid artery may now be examined (Figs. 39, 85, 



