NERVOUS CENTRES. (Human Anatomy. Tue Menryces.) 
The ganglions are small masses occupying 
certain situations in the body. They are ex- 
tremely numerous in the human body, and very 
variable in shape and size. Que great sub- 
division of them, in man and the mammalia, 
_ 48 connected with the posterior roots of the 
7 inal, and with certain encephalic nerves. 
. class belongs to the sympathetic sys- 
tem. In the Invertebrata the nervous system 
is made "p of a series of them variously dis- 
_ posed, with their afferent, efferent, and con- 
necting nerves. 
_ The spinal cord and the brain are peculiar 
to the great class of vertebrated animals. They 
may be regarded as compound ganglions, being 
_ physiologically resolvable intoa series of smaller 
centres, which are, to a certain extent, inde- 
——— of each other. Viewed anatomically, 
; are not so obviously divisible: in the 
> m cord, in which the independent influence 
‘Of separate segments may be most easil 
_ demonstrated, no Siiomixal subdivision x 
obvious, for the segments are fused together 
“Into a cylindroid body, which has a certain 
_ elation to the length and muscular activity of 
the animal. Indications, however, of this 
ite form of the spinal cord are afforded, 
marked difference of dimensions which 
ain parts of it present when compared with 
hers being always a manifest corres- 
‘a 2 between the size of any segment of 
the cord and the motor or sensitive endowment 
__ Of that segment of the body which receives its 
erves from it. And the case of the common 
nard ( Trigla Lyra) may be here quoted as 
markable instance of the developement of 
act gangliform bodies on a portion of the 
cord, in accordance with a particular exaltation 
_Of tactile sensibility. 
The brain is much more evidently made up 
Of a series of separate centres or smaller masses, 
exhibiting sufficiently distinct boundaries on 
uurfaces, but so intimately connected by 
what are called commissural or uniting fibres, 
as to manifest the same kind of fusion (although 
to a less degree) as that noticed in the spinal 
d. These gangliform bodies are so readily 
nguishable from one another, that from the 
i iods of anatomical investigation each 
been designated by a distinct name, 
is generally derived from some prominent 
of the body itself, or from the name of 
ye familiar object which it has been sup- 
_ posed (often fancifully) to resemble. The 
_ aggregate of these bodies is known in popular 
Tangy by the name of Brain, (a word of 
_ Saxon origin, sometimes used in the plural); 
¢ this word, however, anatomically speaking, is 
licable only to the great hemispheric lobes 
lich form the largest portion of the whole 
Mass; and the term Encephalon may be more 
correctly used to denote the whole of the intra- 
en contents. 
_ At is proposed in the present article to con- 
sider the general and uncriptive anatomy of 
these hervous centres severally, beginning with 
examination of their coverings. 
Covertnes oF THE NERVOUS CENTRES. 
ERINGS OF THE GANGLIONS. — Every 
627 
ganglion is covered by a more or led dense 
layer of white fibrous tissue, similar to that 
which forms the neurilemma of nerves. It per- 
forms precisely the same office for the elements 
of the ganglions that the neurilemma does for 
those of nerves; that is, it gives them a me- 
chanical support, and is the medium through 
which bloodvessels are conveyed to their ner- 
vous matter. It is continuous with the neu- 
rilemma of the nerves which are connected 
with the ganglions. It is found in all forms and 
classes of ganglions, presenting the same essen- 
tial characters. These bodies are generally 
surrounded by and imbedded in a considerable 
quantity of fat, which also involves more or less 
the nerves that proceed from them. 
CovERINGS OF THE SPINALCORD AND BRAIN. 
—These are also called the membranes of these 
centres, or the meninges (jmvsyé, membrana). 
They are three in number. Those of the brain 
are continuous with those of the spinal cord, 
but, as there are certain distinctive characters 
proper to each, it will be convenient to describe 
the cerebral and spinal meninges separately. 
They are, enumerating them from without in- 
wards, the dura mater, the arachnoid mem- 
brane, and the pia mater. 
The term, mater, pnTne, originated with the 
Arabian anatomists, who regarded these mem- 
branes as the parents of all others in the body. 
Galen adopted the word pny, and distin- 
guished the first and last of the membranes 
above enumerated by the adjectives rayutegn 
and Aswrn. The Germans use the word haut, 
and designate these membranes as hautige 
Hullen des Gehirns und des Ruckenmarkes ; 
die harte Hirnhaut, die harte Ruckenmark- 
haut, the dura mater of the brain and spinal 
cord; die Spinnwebenhaut, the arachnoid ; and 
die weiche Haut, the pia mater. 
Dura mater —The dura mater is a dense 
membrane com almost exclusively of 
white fibrous tissue. It has all the characters, 
physical and vital, of that texture, possessing 
great strength and flexibility with but little 
elasticity. It is freely supplied by blood- 
vessels, and at certain situations, which will 
be more particularly described by-and-bye, 
it separates into two lamine, which inclose 
prolongations of the lining membrane of the 
venous system, forming peculiar sanguiferous 
channels, which are commonly known by the 
name of sinuses. It has an apparent lamellar 
disposition, from the fact of its fibres being 
arranged in different planes. In the child a 
subdivision into two layers may sometimes be 
easily effected. Some nerves have been de- 
monstrated in the dura mater; a branch of the 
fifth nerve has been particularly described and 
delineated by Arnold, as passing in a recur- 
rent course between the laminz of the tento- 
rium, and Pappenheim has found nervous 
fibres in the cerebral dura mater derived from 
the superior maxillary division of the fifth, 
from the fourth nerve, from the vidian, and 
probably also from the frontal branch of the 
ophthalmic.* 
* Valentin Repertorium, vol. v. p. 87. 
232 
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