Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 2: Dia-Ins
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25760/304/
296 
FIFTH PAIR OF NERVES. 
a more particular account of it necessary than 
would otherwise be required. The chorda tym- 
pani—a delicate filament—is given off from the 
portio dura shortly before that nerve escapes 
from the aqueduct of Fallopius, behind and be¬ 
low the tympanum : it passes upward and for¬ 
ward toward the tympanum, contained in a spe¬ 
cial canal of the bone, and having reached the 
back of the chamber it emerges from its posterior 
wall through a small aperture beneath the base 
of the pyramid; it then attaches itself to the 
outer wall of the tympanum and crosses it 
toward the anterior, having first received * a 
delicate filament from the sympathetic, and 
running forward, upward, and outward. During 
its course from the posterior to the anterior 
wall it is situate at first beneath the short crus 
of the incus, then between the long crus of 
the incus and the superior part of the handle 
of the malleus, to which it is connected by the 
lining membrane of the tympanum. Having 
ascended above the internal muscle of the 
malleus it changes its direction and runs down¬ 
ward, forward, and inward along the superior 
anterior part of the circumference of the mera- 
brana tympani, until it has reached the anterior 
wall of the chamber, from which it goes out 
through the Glaserian fissure, along the tendon 
of the anterior muscle of the malleus. It is 
throughout excluded from the interior of the 
tympanum by the lining membrane, which is 
connected to it upon that side ; it is therefore 
incorrect to say that it crosses the chamber. 
Atter its escape from the tympanum the nerve 
continues to descend forward and inward in 
front of the levator palati muscle, and after a 
course from three-fourths of an inch to an inch 
long it is attached at a very acute angle to the 
back of the lingual branch, becomes inclosed 
in the same sheath with the nerve, and con¬ 
tinues connected with it altogether until the 
nerve has reached the posterior extremity of 
the submaxillary gland : at that point the 
chorda tympani divides into two parts, one of 
which is despatched to the submaxillary gan¬ 
glion, and the other continued along with the 
lingual branch. By somef it is stated that it 
separates from the nerve at the ganglion, and 
is altogether ununited to it ; this, however, is 
incorrect. During its descent in company with 
the lingual branch there may be observed, 
upon particular examination of the conjoined 
trunk, a communication and identification be¬ 
tween the nervous matter of the two nerves. 
Originally the chorda tympani was regarded 
as either a recurrent filament of the lingual 
branch of the fifth or a branch of the portio 
dura : afterwards the opinion was adopted that 
it was not a branch of the portio dura, but the 
cranial superficial petrous branch of the Vidian 
nerve, which, instead of uniting and being iden¬ 
tified with the portio dura, descended through 
the aqueduct merely in apposition with it or 
within the same sheath, separated from it again 
before the nerve escaped from the aqueduct, 
and constituted the chorda tympani. This view 
* Bock, Meckel junior, Cloquet. 
t Cloquet. 
of the nature of the chord, suggested first, as it 
would appear, by J. Hunter, has been advo¬ 
cated also by Cloquet and Hirzel, and is at 
present entertained by many in this country at 
least; it has been objected to by Arnold, and 
another has been advanced by him from obser¬ 
vations made upon the calf and the human 
subject. Hunter’s account of the connection 
of the nerves is as follows : “ This nerve com¬ 
posed of portio dura and the branch of the fifth 
pair sends off, in the adult, the chorda tympani 
before its exit from the skull, and in the foetus, 
immediately after. The termination of the 
branch called chorda tympani I shall not de¬ 
scribe, yet I am almost certain it is not a 
branch of the seventh pair of nerves, but the 
last-described branch from the fifth pair,” i. e. 
the Vidian, “ for I think I have been able to 
separate this branch from the portio dura, and 
have found it lead to the chorda tympani ; per¬ 
haps is continued into it ; but this is a point 
very difficult to determine, as the portio dura 
is a compact nerve, and not so fasciculated as 
some others are.”* According to Arnold, nei¬ 
ther of the previous opinions is correct ; but 
the petrous nerve anastomoses with filaments 
of the facial nerve, principally the external, 
with which it forms a gangliform swelling at 
the place at which the nerve receives it ; and 
the branch which forms the corda tympani 
arises from the gangliform swelling of the facial 
nerve, and holds in an intimate manner to the 
petrous nerve ; however it is not to be consi¬ 
dered a continuation of the latter : it is united, 
during its course, to the facial nerve by several 
filaments, and consequently the chorda tympani 
ought to be regarded neither as a branch of the 
facial nerve nor as a continuation of the petrous 
nerve, but as one composed of both.f Cru- 
veilhierj maintains that the chorda tympani is 
not a prolongation of the Vidian nerve, but he 
assigns no reason for his opinion. The ques¬ 
tion at issue probably cannot be decided from 
the human subject: the impediment opposed 
to its satisfactory determination by the density 
of the facial nerve, as admitted by Hunter, and 
by the manner in which the facial and the 
Vidian nerves are in it blended together at their 
junction, will hardly permit the point being 
accurately ascertained ; but the same diffi¬ 
culty does not exist in other animals, and 
if the disposition of the Vidian nerve at its 
junction with the facial be examined, in the 
horse e. g., no doubt will remain that, 1. the 
Vidian nerve certainly does not run simply in 
apposition with the facial nerve, and, 2. the 
chorda tympani is certainly not a mere conti¬ 
nuation of the Vidian nerve. In the horse the 
facial nerve is much less dense, and more easily 
analyzed than in man, and at the point of junc¬ 
tion with the Vidian its filaments are so free 
and so loosely connected, that little more is re¬ 
quired than to open the packet without violence 
in order to display satisfactorily the disposition 
of the Vidian at its junction with the facial : the 
* Animal (Economy, p. 267. 
f Journ. Compl. t. xxiv. p. 339, 341. 
j Anatomie Descriptive.
        

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