Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Todd, Robert Bentley
646 NERVOUS SYSTEM. (Nervous Centres. Grey Nervous Matter.) 
Fig. 370. 
Dura mater of part of the spinal cord laid open to 
show the ligamentum dentatum. 
dddd, dentated processes. On the right the 
roots of the nerves and the ganglia of the p^steiior 
roots are retained. 
all the characters of white fibrous tissue, of 
which it is chiefly composed. In its dentated 
processes, however, a considerable quantity of 
yellow fibrous tissue may be found. The simi¬ 
larity of its constitution with that of the pia 
mater evidently justifies its being regarded as a 
process of that membrane, and not, as some 
anatomists thought, of the dura mater, with 
which it has a much less intimate and extensive 
connexion. Its anterior and posterior surfaces 
are uncovered by any membrane; they are 
smooth, and have the glistening silvery appear¬ 
ance of white fibrous membrane. It is evident 
that during life these surfaces must be bathed 
by the subarachnoid fluid. 
The office of this remarkable structure seems 
evidently to be mechanical ; to preserve the 
spinal cord in a state of equilibrium ; and to 
prevent lateral movement of it, whilst at the 
same time it forms a partition between the 
roots of the nerves. 
General remarks on the structure of\ the 
nervous centres.—It has already been shewn in 
a former part of this article that the nerves 
properly so called are composed exclusively 
of one kind of nervous substance,—namely, 
the fibrous nervous matter, which is disposed in 
bundles of peculiar fibres. It is only in the 
nervous centres or in continuations of them 
that we find an union of the white and the grey 
nervous matter; and, indeed, it may be stated 
in general, that the peculiar and distinctive 
anatomical character of a nervous centre con¬ 
sists in this combination of the two kinds of 
nervous matter. 
In the nervous centres the white matter exhi¬ 
bits, for the most part, the same essential cha¬ 
racters of structure as in the nerves ; that is to 
say, it is disposed in tubes containing a certain 
pulpy matter in them. It has been found, how¬ 
ever, that these tubes are much more prone to 
become varicose under the influence of pressure 
or of any other disturbing cause. They are 
not, as in the nerves, bound together by areolar 
tissue, but are disposed in bundles and on 
different planes, with their nutrient bloodvessels 
ramifying among them, and in some situations 
the elements of the grey matter are interposed 
between them. Certain parts of the nervous 
centres are composed exclusively of white 
matter, as a portion of the hemispheres of the 
brain, and of the cerebellum, and the superficial 
parts of the spinal cord. 
The white fibres which are found in the ner¬ 
vous centres may be distinguished according 
to their physiological office into four different 
kinds. Two of these are continuations of the 
fibres of the nerves, and serve to connect the 
nervous centres with other organs or textures, 
either by conveying the influence of the centres 
to them, or by propagating impressions from 
them to the centres. The former are called 
efferent, the latter afferent fibres. In addition 
to these, we find a third and large series of fibres, 
which serve to establish a connection between 
different centres, or between different portions of 
the same centre. These are called commissural 
fibres ; they form a large portion of the mass of 
the brain and spinal cord. And Henle suggests 
t! at the brain contains a fourth series of fibres, 
associated with the operations of thought. 
We remark in the nervous centres, especially 
in the brain and spinal cord, a greater difference 
as regards size between the different nerve tubes, 
than may be observed elsewhere, and it seems 
to be a constant character that they diminish


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