, 
) 
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NERVOUS CENTRES. (Human Anatomy. Tut GanGtions.) 
only by the movement of the nucleus, which is 
the consequence of it. * * * In proportion as 
the granular mass contracts itself within certain 
limits, (sich immer mehr abgrenzt,) a cell-mem- 
brane probably becomes developed around it, 
so that the vesicle gradually acquires its precise 
form and size, and its contents their proper 
characters, which belong to a fully formed cen- 
_ tral nervous corpuscule.* Valentin compares 
_ the developement of these vesicles to that of 
the ovum. The nucleolus of the nerve-vesicle 
is always first formed, then around it the primi- 
tive cell, and around this the outer cell. This 
process resembles exactly that which takes 
place dunng the formation of the ovum, for the 
_ germ corresponds to the nucleolus, the germina! 
_ vesicle to the nucleus, the yolk to the contents 
_ of the outer enveloping cell, and the vitelline 
membrane to the delicate wall of this cell, sup- 
_ posing that this latter membrane always exists. + 
_ The great simplicity in the form of the ele- 
“ments of the grey nervous matter is one of its 
Most remarkable characteristics. That a tissue, 
which, as will be shown by-and-bye, plays so 
“prominent a part in the nervous actions, whether 
they are prompted by mental change, or are 
purely corporeal, should exhibit scarcely any 
‘More complexity of structure than that which 
textures, or in structures that have not passed 
fen, in the simplest animal or vegetable 
_ their earliest phase of developement, is an ana- 
_ tomical fact pregnant with great physiological 
interest. Have this simplicity of form and de- 
. 2 
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{ 
__ licacy of structure reference to the celerity of 
the 
> 
‘a 
hervous actions? or to that proneness to 
ge which must be induced by the constant 
“and unceasing round of impressions which the 
"grey matter must receive from the ordinary nu- 
trient actions that are going on in the body, as 
‘well as from the continual action of thought? 
Tf, according to common acceptation, we ad- 
‘mit that the mind is in immediate connexion 
with the cerebral convolutions, it may well be 
imagined that no part of the frame can be the 
‘seat of such active change, from its being on the 
‘one hand the recipient of impressions from the 
body, and, on the other, from an association with 
the nl principle so intimate that probably, 
u ordinary circumstances, an affection of 
the one cannot occur without being communi- 
cated to and producing a change in the other. 
_ Another curious fact, in connexion with the 
imtimate structure of the grey nervous matter, 
is the large quantity of pigment or colouring 
matter which exists in it, and which appears 
to form one of its essential constituents, more 
abundant in some situations than in others, 
but present in all. We are utterly ignorant 
of the design of this peculiarity of structure. 
If this pigment bear any resemblance of che- 
nical composition to the colouring matter of the 
» hematosine,—and it is not improbable 
that it does,—an increased interest attaches to 
the el importance of minute attention, 
on the part of practitioners, to avail themselves 
oo in Soemmering vom Baue, &c. t. iv. 
+ Loe. cit. § 25. 
649 . 
of all the means which are capable of impro- 
ving that important element of the nutrient 
fluid both in quantity and quality, for it is 
most reasonable to presume that the pigment 
of the nervous matter would derive its nou- 
rishment from that of the blood. 
It may be further remarked that pigment oc- 
curs in connexion with the nervous system in 
another form besides that of incorporation with 
its elementary particles, that is, upon the exte- 
rior of parts of the nervous centres or of parti- 
cular nerves. Examples of this may be re- 
ferred to in the case of the olfactory nerve of 
the sheep and of other Mammalia, the bulb 
of which is surrounded by black pigment con-* 
nected with the pia mater. It is also found 
sometimes on the pia mater of the spinal cord 
of the human subject. Valentin, who deli- 
neates a magnified view of this pigment, states 
that it occurs chiefly in the cervical region. In 
frogs, the whole spinal cord and encephalon 
are covered with a silvery pigment interspersed 
with black. The same occurs in fishes. The 
black pigment in connexion with the retina has 
an obvious use. On the choroid gland of fishes, 
which lies immediately contiguous to the re- 
tina and surrounds the optic nerve, there is a 
silvery membrane which contains a quantity of 
the same kind of pigment as that alluded to 
upon their nervous centres. On some of the 
ganglia of the invertebrata particles of pig- 
ment are likewise found. 
Of the structure of ganglions——The descrip- 
tion of the minute anatomy of ganglions as 
well as of all other nervous centres may be 
regarded as the solution of the following pro- 
blem: to determine the relation which the 
white substance of these centres bears to the 
grey matter on the one hand, and to the nervous 
trunks connected with them on the other hand. 
The white substance of the ganglions con- 
sists of a series of minute nerve-tubes, as well 
as of some gelatinous fibres, which are conti- 
nuous with those which exist in the nerves 
themselves. If we trace a nerve into a gan- 
glion, it is found to break up into its com- 
ponent nerve-tubes, and it does so by a se- 
paration of the tubules within into smaller 
bundles, or single tubes. Sometimes adjoining 
bundles interlace, each yielding to its neigh- 
bour one or more tubes. The nerves which 
emerge from the ganglia derive their component 
nerve-tubes from different bundles, so that the 
same kind of interchange of tubules, which we 
have noticed as taking place in plexuses, occurs 
also in ganglia. The emerging nerves result 
from a further subdivision and greater inter- 
mixture of the bundles of nerve-tubes which 
enter the ganglions. The arrangement is well 
shown in fig. 373, where the nerve (a), which 
enters the ganglion, may be seen breaking up 
into a plexus, from which three branches (), 6, 
b) emerge, and it may be observed that these 
emerging nerves derive nerve-tubes from very 
different and opposite parts of the ganglionic 
plexus. In the meshes, which are left be- 
tween the interlacing nerve-tubes, the gangli- 
onic globules or nerve-vesicles are situate (figs. 
373, 374). Certain fibres, according to Valen- 
