THE CRANIAL OR ENGEPHALW NERVES. 829 



Course and Termination . — The great petrosal nerve, after beinj? detached from 

 the facial, and forming with it an obtuse angle opening outwards, entera the 

 aqueduct of Fallopius — a small passage running from behind forward, in the 

 substance of the pt'trons bone, above the. fenestra rotunda and cochlea. Arriving 

 at the interior of the cavernous sinus — which it passes through, inimereed in the 

 blood lliat sinus contains — it receives a branch from the ganglionic plexus there, 

 is lodged in the Vidian fissure, then in the Vidian canal, and in this manner 

 gains the orbital hiatus, where it separates into several l)ranches — most frequently 

 two — which join the posterior part of Meckel's ganglion. It constitutes the 

 motor root and sympathetic ti lament of that ganglion. 



2. Small Superficial Petrosal Nerve. — A very thin filament detached 

 from the facial to the outside of the preceding, and likewise traversing the 

 petrous bone from behind to before, to enter the otic ganglion, as its motor root. 



;-5. Filament of the Stapedius Muscle (Tympanic). — The facial nerve, 

 in its passage above and in front of the stapedius muscle, closely adheres to it, 

 and gives it one, perhaps several, extremely short filaments. 



4. Chorda Tympani (Fig. 459, G). — This filament — also named the tympam- 

 lingiuil nerve — arises at a very obtuse angle from the facial, near the external 

 orifice of the aqueductus Fallopii ; but in reality it comes from the trigeminus. 

 It penetrates the cavity of the tympanum by a particular opening, courses from 

 its posterior to its anterior wall in describing a ciTve downwards, and passes 

 among the chain of auditory bones, between the handle of the malleus and long 

 branch of the incus. Escaping from the middle ear by a canal {fissura Glaseri) 

 on the limits of the mastoid and petrous portions of the temporal bone, it proceeds 

 forwards and downwards, and finally joins the gustatory nerve after a short course 

 beneath the external pterygoid muscle, outside the guttural pouch. 



It is distributed with the lingual in the mucous membrane of the anterior 

 portion of the tongue, and even, according to Vulpian, in the muscles of that 

 organ ; as stimulation of the chorda tympana causes movement of the tongue 

 several days after division of the great hypo-glossal nerve. That physiologist 

 attributes to it all the phenomena that Claude Bernard had observed in the 

 submaxillary gland, after stimulation of the ganglion of that name — vaso-dilating 

 and excito-secretory effects. Consequently, the choroda tympanum should throw 

 a certain number of fibres iu that ganglion, and from it into the gland. 



5. Anastomosing Branch of the Pneumogastric Nerve. — {See the 

 descrifftion of the tenth pair.) 



6. Occipito- Styloid Nerve (Fig. 453, 3). 



7. Stylo-hyoid Nerve. 



8. Digastric Nerve (Fig. 453, 4). — These three spring from a common 

 fasciculus at the stylo-mastoid foramen, and ramify in their respective muscles, 

 after a certain course beneath the parotid gland. 



9. Cervical Branch (Figs. 453, 6). — This nerve has its origin almost in 

 the middle of the subparotideal portion of the facial, near a particular loop 

 thrown by that nerve around the posterior auricular artery, and often from this 

 loop itself. 



It afterwards traverses the parotid gland from within to without, and above 

 to below, to descend at first on its external face — beneath the parotido-auricularis 

 muscle — then into the jugular channel, where it is lodged below the deep face or 

 in the substance of the panniculus muscle, which receives its terminal divisions 

 near the anterior appendix of the sternum. 

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