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/lit25760/317/
309 
FIFTH PAIR 
more remarkable, has been reported by Mr. 
Bishop,* in which the functions of the fifth 
nerve seemed altogether obliterated by the 
pressure of a diseased growth within the 
cranium, and yet the patient saw distinctly 
to the last, the only derangement which oc¬ 
curred in the function of vision being the loss 
of the power of distinguishing colours, which 
appears sufficiently accounted for by a certain 
degree of pressure exerted by the tumour upon 
the optic nerve. Magendie endeavours to 
support his views upon this and other points 
connected with the properties of the nerve by 
reference to a case reported by Serres, which 
appears very inadequate, and will be discussed 
by-and-bye. 
Influence of the fifth nerve on hearing.— 
The great affinity between the sense of hearing 
and that of touch renders it more easy to 
conceive how hearing might be excited through 
the medium of the fifth nerve. As we have 
seen that the ocular nerve in certain animals is 
a branch of the fifth nerve, so is the auditory. 
Among the cartilaginous fishes there are several 
instances in which this occurs. The origin of 
the auditory nerve from the fifth in fishes was 
j, first announced by Scarpa,f and by him sup- 
1 posed to apply to fish generally. This view 
is combated by Treviranus it is admitted 
I in part by Serres; he states that in osseous 
fishes the auditory nerve is united at its in¬ 
sertion with the fifth; in cartilaginous fishes, 
A that the auditoiy is sometimes confounded 
with the fifth, sometimes separated distinctly 
enough, as in the raia clavata. From his own 
observations the writer would say, that in the 
* bony tishes the two nerves cannot be said to 
< be united or to arise the one from the other, 
but only to have a common superficial attach¬ 
ment to the medulla oblongata ; and from the 
analogy of the same nerves in the higher classes 
of animals, he would not admit, without 
further proof, a common superficial attachment 
as establishing identity of ultimate connection 
L with the encephalon. As to the cartilaginous 
fishes, it appears to him that Serres has fallen 
into an error with regard to the connection of 
the auditory nerve. It appears to the writer 
that the fifth and the auditory are con¬ 
founded in the raia clavata as plainly as in 
j. any other individual of the class; the posterior 
ganglionic fasciculus of the fifth and the 
auditory nerve form one trunk for a distance 
of some lines after leaving the medulla ob¬ 
longata ; they are at all events enclosed within 
the same sheath : § but whether they are to be 
regarded as branches of a common trunk or 
not, it is difficult to decide. The weight of 
naalogy is certainly opposed to a conclusion 
* Medical Gazette, vol. xvii. 
J f De Audita et Olfactu. 
1- t Joum. Compl. 
Î § Serres seems to have overlooked the fact that 
there exist two ganglionic fasciculi in the raia 
clavata ; that he has assumed the anterior fasci- 
i cuius to be the fifth, and described the posterior, 
with which the auditory is connected, as the auditory 
and facial nerves : the error will be manifest upon 
tracing the distribution of the fasciculus. 
OF NERVES. 
in the affirmative ; and, though this were ad¬ 
mitted, a difference between the auditory and 
the other branches of the fifth (as supposed) 
must still be admitted, inasmuch as the auditory 
separates from the nerve before the occurrence 
of the ganglion, and has not itself a ganglion. 
On the other hand the auditory may be se¬ 
parated from the rest of the nerve, after the 
division of the common investing membrane, 
with little or no laceration of fibres. Still it 
may be asked why, if they be distinct nerves, 
are they united into one trunk? The opinion 
that the fifth nerve holds an important in¬ 
fluence over the sense of hearing derives support 
from the circumstance, that in most, if not 
all, the cases of disease of the nerve, the 
sense of hearing becomes impaired, though 
not obliterated. 
The last question proposed to be considered 
with reference to the functions of the fifth 
nerve is its connection with nutrition. 
The opinion that the nerve controls the 
nutrition of the parts which it supplies has 
been advocated by Magendie, more particularly 
with regard to the eye. It has been already 
stated that we are indebted to this writer for 
information in regard to results of the division 
of the entire trunk of the nerve within the 
cranium. Of these the most prominent is 
the entire loss of sensibility on the same 
side of the face, and in regard to the eye 
especially, loss of sensibility in the conjunc¬ 
tiva, upon which the most irritating chemical 
agents then produce no impression. These 
immediate effects of the section were followed 
by others not less remarkable : on the next 
day the sound eye was found inflamed by 
the ammonia, which had been applied to it, 
while the other presented no trace of inflam¬ 
mation. Other changes, however, supervene. 
The cornea of the eye of the side on which 
the section is made, twenty-four hours after¬ 
wards begins to become opaque ; after seventy- 
two it is much more so ; and five or six days 
after it is as white as alabaster. On the second 
day the conjunctiva becomes red, inflames, 
and secretes a puriform matter. About the 
second day the iris also becomes red and in¬ 
flames, and false membranes are formed upon 
its surface. Finally the cornea ulcerates, the 
humours of the eye escape, and the globe 
contracts into a small tubercle. In endeavouring 
to ascertain the cause of these changes, Ma¬ 
gendie, on the supposition that they might 
be owing either to the continued exposure of 
the eye to the air or to the want of the 
lachrymal secretion, divided the portio dura 
in one rabbit, the effect of which is to destroy 
the power of closing the eyelids ; and from 
others he cut out the lachrymal gland; but 
in neither case did opacity of the cornea suc¬ 
ceed. The sequence of the effects mentioned 
after the section of the nerve might naturally 
lead us to infer that the loss of nervous in¬ 
fluence gives rise to them. But such is not 
the inference drawn by Magendie, nor indeed 
can it be admitted : absence or subtraction 
of an influence cannot be directly the cause 
of an alteration in the condition of an object
        

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