720u 
the motor nerve to the muscles of the features, 
and to the orbicular muscles of the eyelids. 
Clinical research, indeed, taken in conjunction 
with anatomy, forms the basis of our present 
accurate knowledge of the office of this nerve. 
In like manner we learn that loss of sensibility 
of the face is dependent on disease affecting the 
fifth nerve, and from the parts of the face 
which are affected by anesthesia we can tell 
what portions of that great nerve are diseased. 
Here again anatomy and clinical medicine have 
mainly contributed to the advance of our know- 
ledge. The partial palsies which affect the 
muscles of the eye-ball likewise give very dis- 
tinct interpretation to the functions of these 
nerves, such as the third and sixth, the action 
of whose muscles is well understood. Many 
other instances might be quoted which clearly 
show that, while clinical medicine and anatomy 
are of infinite service in building up and con- 
firming our knowledge of the function of nerves, 
this knowledge, in its turn, does great service 
in increasing the facility with which we can 
distinguish disease. 
Of the functions of the roots of spinal nerves. 
—The greatest part of the bedy is supplied 
with nerves which are implanted in the spinal 
cord, or which, in anatomical language, have 
their origin in that nervous centre. As these 
nerves present very definite and constant cha- 
racters as regards the manner in which they are 
connected with the centre, characters which are 
not limited to the human subject, but which be- 
long to all classes of vertebrate animals, it was 
a point of primary importance to discover the 
object of an arrangement so peculiar as regards 
its anatomical characters, and so universal. To 
our countryman, Sir C. Bell, belongs the great 
merit of having seen the importance of deter- 
mining this point as a preliminary step in the 
investigations into the nervous system; and to 
him must be awarded the credit of having 
achieved the discovery of the difference in the 
endowment of the anterior and of the posterior 
roots of these nerves. He experimented on 
young rabbits, by removing the posterior wall 
of the spinal column. “On laying bare the 
roots of the spinal nerves,” says Sir C. Bell, “I 
found that r could cut across the posterior 
fasciculus of nerves, which took its origin from 
the posterior portion of the spinal marrow, 
without convulsing the muscles of the back ; 
but that, on touching the anterior fasciculus 
with the point of the knife, the muscles of the 
back were immediately convulsed.”’ + 
Numerous experimenters, subsequent to Bell, 
obtained precisely similar results. Muller, 
* Sir C. Bell’s first essay on this subject was 
rinted in 1811. In 1822 Majendie published his 
rst essay in the Journal de Physiologie Exp. t. iii; 
in 1831 Miiller’s experiments were published in the 
Annales des Sciences Nat. and in Froriep’s Notizen. 
Mr. Alexander Shaw has published a temperate 
and judicious vindication of Sir C. Bell’s claims in 
a volume entitled, ‘‘ Narrative of the Discoveries 
of Sir C. Bell in the Nervous System.” Lond. 1839. 
Valentin is so satisfied of Sir C. Bell’s claim to 
the discovery of the distinct endowments of the 
roots of the spinal nerves, that he designates the 
law thereby determined by a title not very eupho- 
nous to English ears, Lex Belliana. 
PHYSIOLOGY OF THE NERVOUS SYSTEM. 
however, obtained the most decisive evidence of — 
the proper functions of the roots of the nerves, 
by experimenting on frogs instead of on mam- 
malia; in the former the spinal canal is of 
great width, especially at its lower part, and 
the roots of the nerves can be exposed with 
great facility, whilst in the latter the operation 
is tedious, painful, and bloody, the spinal 
canal narrow, and the roots of the nerves small 
and difficult to get at. Moreover, the exci 
bility of the nerves lasts very much longer ii 
frogs than in mammalia, and on this account 
the former animals are well adapted for dis- 
playing the effects of section of the roots ant 
the influence of mechanical and other stimu 
upon them. 
In these experiments, (which I have frequent 
repeated with similar results,) irritation, mech 
nical orgalvanic, of the anterior root of the spina 
nerve always provokes muscular contractio 
No such effect follows irritation of the posterio) 
root. Section of the anterior root causes para 
lysis of motion; section of the posterior roo 
paralysis of sensation. This latter effect 1 
shown by the entire insensibility to pain evince 
on pinching a toe, whilst in the limb of whi 
the posterior roots of the nerves remained en 
tire such irritation is evidently felt acutely. | 
the anterior roots of the nerves which are di 
tributed to the lower extremities be cut on ¢ 
side, and the posterior roots on the ot 
voluntary power without sensation will 
in the latter, and sensation without vole 
power in the former. ‘ 
Valentin, Seubert, Panizza, and Longet 
performed similar experiments on mammifero 
animals with precisely similar effects. 
I have never seen motion produced by i 
tation of one of the posterior roots of the spin 
nerves still in connexion with the cord, exce 
ing when the galvanic stimulus has been a 
plied, and too strong a current has been € 
ployed. Valentin states that he has obse 
motions so produced in rabbits, but not in frog 
and tortoises. Dr. Hall has seen them in 
turtle and skate. Van Deen speaks of 
as constantly occurring. But Miuiller denies 
power of the posterior roots to excite mo 
except by “ traction on the cord itself.” 
such effect ever follows any kind of stimula 
of the posterior root when it has been separ 
from the cord. = 
The conclusion which inevitably follows fi 
these experiments is that the anterior rot 
each spinal nerve is motor, and the po 
sensitive. 
Comparative anatomy confirms this ¢0 
sion, by showing that a similar arrangemel 
the roots of spinal nerves prevails amo 
classes of vertebrate animals, and that if in 
particular class either the motor or 
power predominate, there is in correspond 
with it a marked developement of the 
or posterior roots. The frequent occurrer 
likewise, of paralysis of sensation and 
as a consequence of disease within the 
canal, also tends to the same in 
Kronenberg finds a small nerve of ec 
nication between the posterior and the antet 
root, which is looked upon by some as be 
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