THE CRASIAL OR ENCEPHALIC NERVES. 



825 



The ramuscules sent by the sympathetic chain to tlie Gasserian ganglion, are 

 perhaps not foreign to the part the fifth pair seems to play in the secretory acts — 

 nutritive and vaso-motor. 



Jolyet has found in the superior maxillary nerve, vaso-dilator filaments for 

 the mucous membrane of tiie nasal fossae, the skin on tlie wings of the nostrils 

 and lips, and the mucous membrane of the latter and the gums. 



6. Sixth Paie (Abducentes), or External Oculo-motor Nerves (Fig. 450, 5). 



The external oculo-motor 

 behind the pons Varolii, by f 

 to issue from between the 

 inferior pyramid and tlie 

 lateral fasciculus of the me- 

 dulla oblongata (Fig. 424, 9). 

 Its nucleus is confounded with 

 the anterior or superior nu- 

 cleus of the facial, which will 

 be described presently (Fig. 

 454, ME). 



It is directed immediately 

 forward, leaves the pons 

 Varolii in lying close to the 

 inner side of the superior 

 maxillary nerve, and traverses 

 the foramen lacerum orbitale 

 — ^\hich already lodges the 

 ophthalmic branch of the 

 fifth pair and the common 

 oculo-motor nerve — to pierce 

 the bottom of the orbit. It 

 is entirely expended in the 

 external rectus (or abductor) 

 muscle of the eye, after giving 

 off a small ramuscule to the 

 external portion of the re- 

 tractor muscle. 



arises from the medulla oblongata, immediately 

 rom five to eight converging roots, which appear 



DIAGRAM OF A SECTION OF THE MEDUr.LA OBLONGATA AND 

 PONS VAROLII OF MAS, AT THEIR JUNCTION. 



PP, Pyramids; Pr, Pr, transverse fibres of the pons V^arolii 

 (between the various layers of these fibres are irregular 

 strata of masses of grey substance); ME, ME, loots of the 

 external niotores oculorum ; M, nucleus coiiimnn to the 

 external motores oculorum and facial nerve; V^ ^ fasciculus 

 teres (vertical portion of the genu facialis) ; Fi, inferior 

 nucleus of the facial, in which arise the radicles that 

 f"rm the fasciculus teres; GP, gelatinous substance of 

 Rolando (head of the posterior cornu) ; T, ascending or 

 sensitive root of the ti-igeminus ; A'C, grey substance on 

 the floor of the fourth ventricle (nucleus of the auditory 

 nerve): AG. auditory nerve; e, external root of ditto; 

 I, internal root of ditto ; xx, raphe ; OR, restiform body. 



7. Seventh Pair (Portio Dura), or Facial Nerves (Figs. 453, 454). 



The facial is a nerve exclusively motor at its origin,^ but it becomes mixed, 

 during its course, by the addition of several sensitive branches. 



Origin. — It emanates from the medulla oblongata, immediately behind the 

 pons Varolii, and appears to originate at the external extremity of the transverse 

 band that margins the posterior border of that protuberance. But if we attempt 

 to trace its origin in the substance of the medulla oblongata, we see the single 

 fasciculus it constitutes, at its point of emergence, descend into the groove 

 between the pons Varolii and the above-mentioned band ; it then traverses 

 nearly the whole thickness of the medulla, passing between the lateral cord or 



' See hereafter the description of the great petrosal nerve, for an account of the constitution 

 of the facial nerve. 



