TllE I'ACIAL .\ERVE 975 



beneath the eminent la medialis. and it is in direct linear series with the nnelei of the 

 third, fourth, and twelfth nerves. The (Hires which pass from the nucleus into 

 the sixth nerve run interiorly and ventralwards through the reticular format ion, the 

 trape/ium, and t he ])yramidal fibres, and they emerge from t he ventral surface of t lie 

 medulla in the sulcus between the lower border of the pons and the upper end of the 

 pyramid of the medulla. From this superficial attachment I he nerve runs upwards 

 and forwards in tin; subarachnoid space between I he pons and the basisphetioid and 

 at the side of the basilar artery. A little below the level of the upper border of the 

 petrous portion of the temporal bone it pierces the dura mater, pa>.-es beneath the 

 petro-sphenoidal liniment, at the side of the dorsum selhe, and enters the cavernous 

 sinus, in which it runs forwards alon.ir the outer side of the internal carotid artery. 

 At the anterior end of the sinus it passes through the superior orbital (sphenoidal) 

 fissure between the heads of the reel us lateralis, below the lower division of the 

 oculo-motor nerve, and above the ophthalmic' vein. In the orbit it runs forwards on 

 the inner or ocular surface of the reel us lateralis, and finally it pierces this muscle and 

 ends in its substance. 



While it is in the cavernous sinus it receives communications from the carotid 

 plexus of the sympathetic and from the ophthalmic nerve. 



All the fibres arising in the nucleus of the sixth nerve do not pass into the sixth nerve. Some 

 of them ascend in the medial longitudinal fasciculus, cross the mid-line, and join the third nerve 

 of the opposite side, by which they are conveyed to the opposite internal rectus muscle. Thus 

 impulses starting from the sixth nerve nucleus can throw into simultaneous action the external 

 rcci us <if the same side and the internal rectus of the opposite side, and thus turn both eyes in the 

 same direction. 



Central Connections. The nucleus of the sixth nerve is connected with the somiesthetic 

 areaof the opposite side by the pyramidal fibres, and it is associated with the sensory nuclei of 

 other nerves by way of the medial longitudinal fasciculus (p. 800). 



THE SEVENTH NERVE THE FACIAL 



Like the trigeminus, the seventh or facial nerve is a mixed nerve. Each possesses a 

 sensory, ganglionated and a motor, non-ganglionated root, but the double con- 

 dition of the seventh is somewhat masked by the fusion of the two roots both on the 

 inner and on the outer side of the ganglion, which is situated, therefore, on the trunk 

 of the nerve. The ganglion is relatively small and its cells give origin, of course, to 

 only the sensory root or pars intermedia, which is smaller than the motor root. 



The Motor Root and the Trunk. The fibres of the motor portion of the seventh 

 nerve spring from a nucleus of cells situated laterally in the reticular formation of the 

 lower part of the pons. dorsal to the superior olive, and between the root fibres of the 

 sixth nerve and the laterally placed spinal tract of the trigeminus. From this nucleus 

 the fibres of the nerve pass medially and dorsalwards to the floor of the fourth ven- 

 tricle and, just under the floor, they turn anteriorly, passing dorsal to the nucleus of 

 the abducens (fig. 603, p. 811). At the anterior end of this nucleus they turn sharply 

 ventralwards and lateralwards, and at this point it is claimed that fibres descending 

 in the near 1 >y medial longitudinal fasciculus from the nucleus of t he oculo-motor nerve 

 of the same side become intermingled with the fibres of the facial nerve and pass 

 outwards with them. Continuing ventralwards through the reticular formation 

 the fibres of the facial emerge from the brain-stem at the inferior border of the 

 pons, lateral to the superficial attachment of the abducens. At the point of its 

 emergence, the facial nerve pierces the pia mater, from which it receives a sheath, 

 and then proceeds forwards and outwards in the posterior fossa of the cranium to t he 

 internal auditory meat us. which it enters in company with its pars intermedia and with 

 the eighth nerve. As it lies in the meatus it is situated above and in front of the eighth 

 nerve, from which it is separated by the pars intermedia, and it is surrounded, to- 

 gether with the pars intermedia and the eighth nerve, by sheaths of both the arachnoid 

 and the dura mater and by prolongations of the subarachnoid and sub-dural spaces. 

 While it is still in the meatus it blends with the pars intermedia and thus the com- 

 plete trunk of the facial nerve is formed. At the outer end of the canal the trunk 

 pierces the arachnoid and the dura mater and enters the facial canal (aqueduct ot 

 Fallopius), in which it runs forwards and slightly outwards to the hiatus Fallopii. 

 where it makes an angular bend, the </< iiiculinn. around the anterior boundary of the 

 vestibule, and this bend is enlarged by the formation of the geniculate ganglion in its 



