PHYSIOLOGY OF THE NERVOUS SYSTEM. 
the means of giving to the anterior root the 
slight degree of sensitive power which Majendie 
attributes to it. 
From the determination of the office of each 
root of the spinal nerves we obtain the further 
important result, that the nerve, which is formed 
by the junction of these two roots, is sensitive and 
motor, and that nervous fibres of different en- 
dowments may be bound together in the same 
sheath constituting one nerve, which is com- 
pound in its functions. And the anatomical 
distribution of spinal nerves, both in man and 
the inferior animals, to the muscles and sen- 
sitive surfaces of the trunk and extremities, is 
entirely confirmatory of the results thus derived 
from experiment. 
By the use of the various means for deter- 
mining the functions of nerves, above detailed, 
and aided by the determination of the law dis- 
covered and developed by Bell and others, 
as to the motor nature of the anterior and the sen- 
sitive endowment of the posterior roots, and the 
subsequent binding together of these fibres in one 
sheath to form a compound nerve, physiologists 
have made great advances in determining the 
functions of the various encephalic nerves, and 
our knowledge on this subject may be said to 
have approached more to perfection than that 
of any other physiological questions. The main 
facts connected with the anatomy and _ physio- 
logy of each of these nerves will be found under 
the articles headed by their names. 
Of the functions of the nervous centres.— 
In examining into the functions of the va- 
rious parts of the cerebro-spinal axis I shall 
adhere to the definitions already adopted in the 
previous part of this article, and use the term 
spinal cord as denoting the nervous cylinder 
within the spinal canal, and the encepha/on as 
the intra-cranial mass, consisting of medulla 
oblongata, mesocephale, cerebellum, and cere- 
brum. ; 
Of the functions of the spinal cord.—It was 
long held that the spinal cord was no more 
than a bundle of nerves proceeding from or to 
the brain, and emerging at various points of 
the vertebral canal to be distributed to their 
destined regions.* 
The anatomy of the organ, however, suffi- 
ciently exposed the error of this opinion. The 
| existence of a large quantity of vesicular matter 
in it varying in quantity according to the bulk 
of its segments showed that it was more than a 
mere fasciculus of nerves. Although the true 
office of the spinal cord was known to physio- 
logists long before, to Prochaska for example, 
Gall appears to have been the first who ad- 
duced the best proofs from anatomy to show 
that the spinal cord was not a mere appendage 
to the brain, but a special centre in itself. His 
principal arguments were derived from the 
want of any constant proportion in bulk be- 
tween it and the brain, the spinal cord being 
small with a large brain, as in man, and large 
with a small brain, as in the inferior mammalia 
and in other vertebrata, from the fact that it 
does not taper gradually in proportion as it 
* That this was Willis’s view a perusal of chap- 
4 Xviii. and xix. of his Cerebri Anatome will 
ew. 
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720x 
gives off nerves, but on the contrary is alter- 
nately large orsmall according to the numberand 
volume of the nerves which are given off from 
its various segments; and, lastly, from the ana- 
logy which he indicated between the spinal 
cord of vertebrata and the ganglionic chain of 
articulata, the former consisting of a series of 
ganglia fused together, the latter remaining 
separate by reason of the peculiar disposi- 
tion of the bodies of these animals in distinct 
segments. 
The determination of the functions of the 
nerves which are intimately connected with or 
implanted in the spinal cord affords some clue 
to the solution of the problem as to its own 
office. There can be no doubt that as the 
nerves of sensation as well as those of motion 
of the trunk and extremities are all, to say the 
least, intimately connected with the cord, this 
organ must be the medium of the reception 
and propagation of the sentient impressions 
made upon the one, and of the mental or phy- 
sical impulses which excite the others. 
If, moreover, we look to the results of expe- 
riments on the lower animals, or to the effects 
of injury or disease in the human body, we 
obtain the following important facts :—1st, that 
the perfect connexion of this organ, in all its 
integrity, with the encephalon is the essential 
condition for the full and complete exercise of the 
nervous force, whether for sensation or voluntary 
motion, as far as regards the trunk and extremi- 
ties; 2nd, that division of the cord, so as com- 
pletely to separate the lower from the upper 
segment, causes paralysis both of sensation 
and voluntary motion in the parts supplied with 
nerves from the lower segment; 3rd, if the 
section be made high up in the neck so as to 
separate the cord from the medulla oblongata, 
all the parts supplied by spinal nerves will be 
paralysed in the same way; by such an expe- 
riment the spinal cord remains entire, but its 
continuity with the encephalon is interrupted. 
In cases of injury to the vertebral column 
it may be laid down as the rule that the higher 
the seat of injury the more extensive will be 
the paralysis. A man whe has received exten- 
sive injury of the spinal cord high up in the 
neck is like a living head and a dead trunk, 
dead to its own sensations, and to all voluntary 
control over its movements. The same rule 
prevails with regard to the effects resulting from 
disease of the vertebre or from any intra-spinal 
growth, or from a morbid state of the cord itself, 
there being only this difference, that where the 
morbid change is chronic, the paralytic effects 
are less marked than in injury or acute disease. 
In all cases the extent of the paralysis affords 
a correct indication of the seat of the solution 
of continuity. ; 
If the spinal cord be divided partially in 
the transverse direction, there will be paralysis 
of parts on the same side with the injury. 
Dr. Yellowly has put on record an experi- 
ment of Sir Astley Cooper’s, in which he 
divided the right half of the spinal cord in 
a dog just above the first vertebra. The effect 
was paralysis of the motions of the ribs on the 
right side, and of the right posterior and pos- 
terior extremities, with irritation of those of 
