NERVOUS CENTRES. (Human Anatomy. Tae Sprxat Corp.) 
the middle line, and that to this cause the in- 
distinctness of the posterior fissure may be due. 
And this anatomical fact may be quoted as, in 
some degree, adverse to the theory which re- 
gards these columns as sensitive: for were they 
columns of sensation, it is probable that the 
reservation of their distinctness would have 
n more fully provided for. 
The anterior and posterior fissures, as Cru- 
veilhier remarks, leaving on each side a per- 
fectly symmetrical organ, serve to demonstrate 
the existence of two spinal cords, one for each 
side of the body, and both presenting a perfect 
resemblance of form and structure. 
_ There are no other fissures in the cord 
_ besides those just described. Several anato- 
mists regard the lines of origin of the anterior 
_and posterior roots of the nerves as constituting 
distinct fissures. But a little careful examina- 
tion will readily convince any one that there is 
no real separation of the nervous substance of 
the cord corresponding to these lines, and that 
1 is no anatomical indication of a sub- 
division into columns or segments in connexion 
with them. When the roots of the nerves have 
been removed on each side, nothing is seen but 
‘a series of foramina or depressions correspond- 
ing to the points of emergence of the nerve- 
fibres, of which the roots are composed. 
_ The most natural subdivision of the spinal 
cord is that which is obviously indicated by its 
internal structure. In examining a transverse 
Section (fig. 376), we observe that the interior 
Fig. 376. 
of each lateral portion is occupied by grey 
_ matter, disposed somewhat in a crescentic form. 
“The concavity of the crescent is directed out- 
wards: its anterior extremity is thick, and is 
‘Separated from the surface of the cord by a con- 
‘siderable layer of white nervous substance. The 
grey matter is prolonged backwards and out- 
wards in the form of a narrow horn, which 
reaches quite to the surface of the cord, and near 
‘the surface experiences a slight enlargement. 
‘This posterior horn constitutes, on each side, a 
natural boundary between the two columns of 
which each lateral half of the cord consists. All 
that is situate in front of the posterior horns is 
called the antero-lateral column, and this com- 
prehends the white matter forming the sides and 
tront of the semi-cord, limited anteriorly by the 
anterior fissure and posteriorly by the posterior 
roots ofthe nerves. The posterior column is 
situate behind the posterior horn of grey matter, 
and is separated from its fellow of the opposite 
side by the posterior fissure. 
_ According to this view, then, the spinal cord 
will be found to consist of four columns, 
between which an obvious line of demarca- 
tion exists throughout the whole length of the 
organ. ese are two antero-lateral columns 
653 
and two posterior columns. The former con- 
stitute by far the largest proportion of the white 
substance of the cord, and they envelope the 
anterior obtuse portion or horn of the grey 
matter. The white commissure at the bottom 
of the anterior fissure unites them. The anterior 
roots of the nerves are connected with them, 
and the posterior roots adhere to them when 
the cord is split up along the plane of the pos- 
terior horn. The posterior columns are small, 
in section triangular, placed in apposition with 
each other by their inner surfaces. Their apices 
are directed forwards, and their bases, which 
are slightly curvilinear, hackwards. No distinct 
commissure of white fibres can be detected 
uniting these columns, save, perhaps, in the 
lumbar region. The connexion of the posterior 
roots of the nerves with them must necessarily 
be very slight, as they invariably separate from 
them in the longitudinal splitting of the cord. 
The arrangement of the grey matter in the 
cord, as already partly explained, is as follows: 
In each lateral half there is a portion of grey 
matter, which is crescentic in form, having its 
concavity directed outwards and its convexity 
inwards towards its fellow of the opposite side. 
The anterior extremity or horn of the crescent 
is thick and roundish, and its margin has a 
jagged or serrated appearance, which is more 
conspicuous in some situations than in others. 
The posterior horn is directed backwards and a 
little outwards: it reaches the surface of the 
cord, and near its posterior extremity it presents 
a swollen or enlarged portion, which differs in 
colour and consistence from the rest of the 
crescent, being somewhat paler and _ softer. 
This portion of grey matter has been called by 
Rolando substantia cinerea gelatinosa. It is 
that part of the grey matter which appears to 
be more immediately connected with the pos- 
terior roots of the nerves. . 
There is an exact symmetry between the 
grey crescents of opposite sides, and they are 
united by means of the grey commissure, a 
layer which extends between the two crescentic 
portions, being attached very nearly to the 
central point of each. This commissure, then, 
when examined in its length, forms a vertical 
plane of grey matter, extending throughout the 
whole of the cord. The lateral portions are 
solid masses of grey matter, with which the 
nerve-tubes of the white substance freely inter- 
mingle, and in which, as in the grey matter 
elsewhere, very numerous bloodvessels ramify. 
There seem to be no good grounds for the opi- 
nion advanced by Mayo that these crescentic 
| ney are hollow capsules. It was supposed 
y this anatomist that each crescent resembled 
the dentated body in the cerebellum or that 
in the corpus olivare; but careful examination 
must convince any one who takes the trouble 
of it that such is not the fact. It is true that 
the grey matter contains white fibres, but they 
mingle with its elements and are not enclosed 
within a layer of it, as described and delineated 
by Mayo. 
When sections of the spinal cord in different 
regions are examined, they are found to exhibit 
differences of dimensions affecting both the white 
