SEVENTH PAIR OF NERVES 



fibres. From the fact of its lesser consistence, 

 it is frequently termed the "portio mollis" of 

 the seventh nerve. 



Its apparent origin is close to that of the 

 facial. At the upper part of the lateral surface 

 of the medulla oblongata, a somewhat trian- 

 gular depression exists, which is bounded in 

 front by the olivary body, above by the lower 

 border of the pons varolii, and behind by the 

 restiform body. This shallow cavity has been 

 termed by Vicq d' Azyr "the fossa of the 

 olivary eminence," and in it appears the com- 

 mencement of the auditory nerve. 



On dissecting out this origin, however, it 

 may be separated into two portions or roots. 

 One of these immediately penetrates the res- 

 tiform body at a right angle to its surface, and 

 sinks into the central grey matter of the me- 

 dulla oblongata : while the other, continuing 

 backwards superficially to the restiform body, 

 winds round it to reach the floor of the fourth 

 ventricle, where this structure is deficient. 

 By this latter root, the nerve seems to be 

 directly continuous with the tranverse white 

 fascicles of the calamus scriptorius ; and near 

 the middle line, it sinks into the posterior part 

 of the same grey mass of the olivary columns, 

 into which the other portion was followed. 



But considerable variations appear to prevail 

 in the degree of the visible continuity of this 

 root with these transverse white striae. Thus 

 Meckel and Prochaska remarked that they are 

 sometimes wanting; while Longet* confirms 

 their statements, and adds, from the experience 

 of himself, Serres, and others, cases which 

 show that not only is their number variable 

 within certain limits, but that, even where 

 present, they may not unite with the root of 

 the auditory nerve, but may curve upwards 

 at their extremity, and pass up the posterior 

 surface of the mesocephale. One or two ex- 

 aminations made by the author of this article 

 seern to show that this is by no means unusual. 



Other and more complicated origins have 

 been ascribed by various anatomists to the au- 

 ditory nerve. Thus, according to Fovillef, a 

 thin and white nervous lamina, which is con- 

 tinued from its roots and from those of the fifth 

 nerve, is spread over, and as it were -lines, the 

 interior of the cortical grey matter of the cere- 

 bellum, in addition to covering the whole sur- 

 face of the fourth ventricle and medullary 

 velum. But in this and other descriptions of 

 a like tendency, it seems difficult to distinguish 

 how much of the connection observed was 

 referrible to a mere physical contiguity of the 

 soft nervous matter, apart from that unbroken 

 continuity of nerve-tubules which we are pro- 

 bably justified in predicating of the cerebral 

 nerves and their more immediate processes of 

 origin. 



From the place of its first appearance at 

 the surface of the encephalon, the nerve 

 passes, in a direction which is at once for- 

 wards, outwards, and upwards, to the inner 



* Anatomie et Physiologic du Systeme Nerveux, 

 torn. ii. p. 84. 



f Traite Complet de 1' Anatomie du Systeme 

 Nerveux Cerebro-spinal. Premiere Partie. 



surface of the petrous portion of the tem- 

 poral bone, where it enters the internal audi- 

 tory meatus. In this course, the flocculus, 

 an isolated lobule of the cerebellum, is in 

 close proximity with its outer side ; while on 

 its inner side, and in front of it, is the portio 

 dura, which slightly grooves this surface of 

 the somewhat flattened auditory nerve. 



After entering the auditory canal, it con- 

 tinues along it to its termination ; and, finally, 

 at the bottom of the meatus, it divides into 

 two branches. The anterior of these is dis- 

 tributed to the cochlea : and the posterior, 

 which exhibits a small gangliform enlarge- 

 ment, supplies the vestibule, dividing into 

 three branches; one for the posterior vertical 

 canal, another for the sacculus, and a third 

 for the utriculus, and remaining semicircular 

 canals. These several divisions perforate the 

 numerous foramina which are found at the 

 bottom of the meatus to enter the internal 

 ear ; but as an account of their further ar- 

 rangement with respect to the parts they sup- 

 ply would require a description of the auditory 

 apparatus itself, the reader is referred to a 

 previous article, " ORGAN OF HEARING," in 

 which these details will be found included. 



The facial nerve, the " portio dura " of the 

 seventh pair, emerges from the same depression 

 in the restiform body which was above de- 

 scribed as giving rise to the auditory. It is 

 of a much firmer and harder consistence than 

 the latter, the tubules which compose it being 

 connected by, and included in, a firm and 

 strong neurilemma. Its real origin is generally 

 referred to that central grey matter of the 

 olivary columns to which so many of the 

 encephalic nerves are traced. It is difficult 

 to follow it any depth beyond these in a satis- 

 factory manner ; but Foville considers that 

 it may be traced in the transverse direction 

 around the olivary column and anterior pyra- 

 mid, and hidden beneath the lower margin of 

 the pons varolii, to an origin from the inner 

 border of the pyramid. He corroborates this 

 by a reference to its comparative anatomy ; 

 and states that the various stages of this course 

 are successively laid bare by that diminished 

 development of the lower arches of the pons 

 which occurs in many of the mammalia. The 

 description given by Morganti* somewhat 

 differs from this, since he describes its roots 

 as radiating by many filaments, ascending, 

 descending, and transverse ; and the latter 

 joining more deeply the central grey substance 

 of the medulla oblongata near the floor of 

 the fourth ventricle. 



The description of the facial nerve may be 

 conveniently separated into three parts : each 

 representing a distinct stage of its course, 

 which is accurately defined by its anatomical 

 relations to the skull. The first of these is 

 intra-cranial, and extends from the surface of 

 the encephalon to the termination of the in- 

 ternal auditory canal. The second is osseous, 

 and reaches from the latter point to the 

 stylo-mastoid foramen, which forms the exit 



* Annali Universal! di Medicina. Giugno, 1845. 



