DISSECTION OF THE BRAIN, OR ENCEPHALON. 255 



The nerve reaches the orbit by passing through the foramen lacerum 

 orbitale. 



The Facial or 7th nerve springs out of the medulla, close behind 

 the pons, its fibres seeming to continue outwards the trapezium. Its 

 rootlets are traceable to nuclei of grey matter in the medulla. The 

 nerve is joined by a delicate filament — the portio intermedia — which 

 appears between the roots of this and the next nerve. The 7th nerve 

 enters the internal auditory meatus in company with the 8th nerve. 

 Separating from that nerve, it passes along a canal in the petrous 

 temporal bone — the aqueduct of Fallopius — from which it emerges by 

 the stylo-mastoid foramen, under the parotid gland. Within the aque- 

 duct of Fallopius the nerve forms a knee-shaped bend, and at that point 

 it shows a minute ganglion — the geniculate ganglion — from which pro- 

 ceed the great and small superficial petrosal nerves (pages 189 and 214). 



The Auditory or 8th nerve springs from the medulla, close behind 

 the pons, and immediately external to the root of the 7th. It is here 

 compounded of two roots — a superior and an inferior. The siqyerior root 

 (Plate 35) passes over the restiform body to the grey matter at the floor 

 of the 4th ventricle. The inferior root springs out of the side of the 

 restiform body, its fibres arising from nerve cells of that body or of the 

 grey matter at the floor of the 4th ventricle, and possibly also from the 

 cerebellum. The 8th nerve enters the intenial auditory meatus, and 

 penetrates to the internal ear. 



The Glosso-pharyngeal or 9th nerve springs out of the side of the 

 medulla, a little behind the outer extremity of the trapezium. It is 

 here compounded of two or three bundles, the outermost being in line 

 with the roots of the next two nerves. The fibres emanate from nerve 

 cells of the grey matter at the floor of the 4th ventricle. The nerve 

 leaves the cranium by the posterior part of the foramen lacerum basis 

 cranii, and at that point it shows a minute ganglion — the petrous 

 ganglion, or the ganglion of Andersch, from which the nerve of Jacobson 

 arises (page 269). 



The Pneumogastric, Vagus, or 10th nerve is formed by a number of 

 rootlets which spring from the side of the medulla, behind and in line 

 Avith the outermost fibres of the 9th nerve. Its fibres arise from nerve 

 cells of the medulla. The nerve passes out of the cranium by the 

 posterior part of the foramen lacerum basis cranii, and is joined by the 

 inner division of the 11th nerve. As the nerve passes through the 

 foramen it presents an enlargement — the upper ganglion, or ganglion of 

 the root. From this ganglion arises the auricular branch of the vagus, 

 which penetrates to the aqueduct of Fallopius, Avhere it anastomoses 

 Avith the 7th nerve ; afterwards emerging from the bone in company 

 with that nerve, to be distributed to the mucous membrane of the 

 external auditory process. 



