652 
part in the new-born infant. The actual weight 
of the spinal cord in an adult male may be 
stated to be a little more than one ounce. 
We may here again notice the interesting 
fact that there is a great disproportion between 
the size of the spinal cord and that of the ver- 
tebral canal, and that consequently a consider- 
able space is found between the cord and its 
membranes which is occupied by the cerebro- 
spinal fluid. 
The consistence of the medullary substance 
of the spinal cord, in the fresh state, is of much 
greater firmness than that of the brain. This 
lasts, however, but for a very short time, for 
decomposition sets in quickly, and then the 
cord acquires a pultaceous consistence, and 
the nervous matter may be easily squeezed out 
of the sheath of pia mater in which it is en- 
closed. 
The pia mater adheres very closely to the 
surface of the cord, as intimately as the neu- 
rilemma to a nerve. In order to examine the 
surface of the cord, the best mode of proceeding 
is to dissect off the pia mater carefully, the 
cord having been fixed under water. The dis- 
sector will then perceive that numerous minute 
vessels, accompanied by delicate processes of 
the membrane, penetrate the cord at all points 
from the deep surface of the pia mater, and to 
this is due the adhesion of this membrane 
above-mentioned. This arrangement may also 
be shewn by dissolving out the nervous matter 
through the action of liquor potasse. The pro- 
longations from the deep surface of the sheath 
may be shewn by floating the preparation in 
water. 
The spinal cord is penetrated both on its 
anterior and posterior aspect by fissures, each 
of which corresponds to the median plane. 
They are separated from each other by a trans- 
verse bilaminate partition of white and grey 
matter, of which the grey layer is posterior. 
This serves to connect the equal and symme- 
trical portions into which the cord is divided 
by these fissures. 
The anterior fissure is very distinct and 
easily demonstrated. A folded portion of the 
pia mater may be traced into it down to the 
commissure. The edges of this fold, as it 
enters the fissure, are connected by a band of 
white fibrous tissue, which may be traced 
through the whole length of the cord on the 
exterior of the pia mater, and indicates pre- 
cisely the position of the anterior fissure, and 
which covers the anterior spinal artery. When 
this fold is carefully removed, the floor of the 
fissure becomes apparent, formed of a lamina 
of white nervous matter. This layer is per- 
forated by a great number of minute orifices, 
which give to it quite the cribriform character, 
and are for the reception and transmission of 
bloodvessels. In many parts the layer appears 
to be composed of oblique and decussating 
fibres, as if the same kind of decussation 
which occurs at the lower part of the medulla 
oblongata extended through the whole length 
of the cord. There is not, however, any real 
decussation : the Cesare of it results from 
the foramina not being always on the same 
NERVOUS SYSTEM. (Nervous Centres. Tue Spinat Corp.) 
level. For, in those places where they lie qui 
on a level with each other, no one could su 
se that such an arrangement of fibres ¢ 
isted. Here, as elsewhere, the fibres 
the transverse direction. The depth of © 
anterior fissure is not the same all down | 
cord ; it gradually diminishes towards its lov 
point ; its deepest part, however, corresponds 
the cervical enlargement, and here it 1s 
one-third of the thickness of the cord me 
from before backwards. 
The whole cribriform layer which f 
the floor of the anterior fissure constitute 
commissure between the lateral halves of 
cord in their whole length. It is callec 
anterior or white commissure of the cord. 
The posterior fissure is vee much finer ; 
more difficult to demonstrate than the ante 
It is not penetrated by a_ fold of the pian 
a single and very delicate layer of that m 
brane is continued from its deep surface d 
to the floor of the fissure. It is at thiss 
tion that the spinal pia mater assumes 
appearance and character of that of the t 
Here and there, within the fissure, the pia m 
appears interrupted and the vessels extre 
few, and in such situations the fissure bee 
very indistinct and difficult to recogr 
process of pia mater becomes extremely 
cate towards the lowest extremity of the 
The posterior fissure is deeper than 
terior. Through a great ie of its 
equal to fully one-half of the thickne 
cord ; in the lumbar region, however, 
is very much less. Its floor is formed 
layer of grey matter, which connects the 
ritious matter of each lateral half of t 
and which is called the grey commi: 
the lumbar region, however, it does 1 
to reach the grey commissure. i 
Arnold denies the continuity of the pos 
fissure through the greater part of the ce 
and dorsal regions. According to his ft 
ceases on a level with the second cerviea 
and reappears about the second dorsal vel 
This does not at all accord with my ok 
nor is it confirmed by any anatomist 
know of. It appears to me that the ¢o 
of the fissure might be more proper 
tioned at the lowest third of the ¢ 
it is often so feebly developed as te 
tection. In three out of four 
before me, the fissure is sufficiently t 
marked down to quite the lowest ex 
the cord, and the posterior columns : 
readily from each other along it. In the 
which is quite recent, the fissure at the 
rt of the cord is only to be distin 
ere and there by a solitary red vess 
ing to the grey commissure, 
distinct in the cervical ion. The 
cimens which shew it well have been 
ened in a preserving liquid, which, t 
stringing the substance of the posterior ¢ 
renders the fissure much more distinct. 
seems little doubt that the posterior co 
have no connexion with each other as far 
as the lumbar region. Below that, hower 
is not improbable that they may be united 
c 
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spec 
