might most legitimately be expected that a 
proportionate developement of these parts 
would exist in the cervical region. Yet a 
_ comparison of the cervical with the lumbar 
swelling demonstrates that the developement 
' of both the grey matter and the posterior co- 
lumns, (if not absolutely, certainly relatively to 
the bulk of the segment,) is inferior in the 
former to that in the latter, whence nerves are 
| supplied to the inferior extremities in which 
Sensibility is much less acute, and in which 
there is a much less perfect adjustment of 
the voluntary power to the muscular move- 
_ ments. 
_ __ The difference of the respective sizes of the 
antero-lateral columns in those parts of the cord 
which supply the upper and lower extremities 
__ is perfectly consistent with the difference in the 
_ sensibility and voluntary power of those parts.* 
And as in the trunk these endowments are 
at their lowest point of developement, so the 
region of the cord is that which exhibits 
the antero-lateral columns of the smallest 
_ In the lower parts of the body, which re- 
ceive their supply of nerves from the lumbar 
Swelling of the cord, there are certain peculi- 
arities worthy of the attention of the physiolo- 
i, Thus the sphincter muscles of both the 
er and rectum are to a great degree inde- 
pendent of voluntary influence, and act inde- 
dently of consciousness. The principal 
ion of the lower extremities is that of 
locomotion; they are the pillars of support to 
the trunk, and the chief agents in the main- 
ance of its attitudes. And, although in 
hese actions the will exercises a not inconsi- 
derable control, still the principle of purely 
physical nervous action renders them in a 
great degree independent of the mind.+ 
the reflex or excito-motory actions are much 
more evident in the lower than in the 
er extremities; the former are much 
ore independent of cerebral lesion than the 
ter. And let it be remarked that these 
phenomena are associated with high deve- 
pement of grey matter, and with posterior 
columns of large size, while the antero-late- 
Tal columns are comparatively small. May 
“not the high developement of the grey matter 
hhave reference to the exalted state of the phy- 
sical nervous actions of the lower part of the 
, and that of the posterior columns to the 
ive actions? To these points we shall 
in to refer when we discuss the func- 
ew the spinal cord. 
Ts there a central canal in the'spinal cord? 
Many anatomists have affirmed that the spinal 
was traversed in its entire length by a 
anal, which was continuous with the fourth 
} ventricle. If such a canal exist, it must be 
| extremely difficult to demonstrate, as I have 
Never, after numberless examinations, been 
* Weber’s experiments sufficiently indicate that 
the general as well as the tactile sensibility of the 
lower extremities is considerably inferior to those 
of the upper extremities. 
t See the observations at the commencement of 
1c article, p. 589, 
NERVOUS CENTRES, (Human Anatomy. Tue Spinat Corp.) 
655 
able to see it. In transverse sections of the 
spinal cord, which have been dried upon glass, 
there is sometimes an appearance which may 
be attributed to the presence o1 4 minute canal ; 
but I should be more disposed to ascribe it to 
the patulous mouth of a bloodvessel which had 
been divided in making the section, for it is 
by no means constant even in different regions 
of the same spinal cord. The situation which 
some have assigned to this supposed canal is 
between the grey and white commissures ; but 
Stilling and Wallack* place it in the grey 
matter. It is obvious that an artificial sepa- 
ration of these layers, which is easily effected, 
and more especially while the preparation is 
being dried, would give rise to the appearance 
of a canal upon a transverse section. It may 
be stated, further, that the deepest part of the 
longitudinal fissure is wider than any other 
portion of it, and, if cut across, might appear 
like a canal. 
The observations of Tiedemann appear to me 
to put this question in its true light. I shall, 
therefore, make the following quotation from 
his learned work on the anatomy of the fetal 
brain, without, however, subscribing to the ac- 
curacy of all the statements it contains. 
“ The spinal marrow,” says Tiedemann, 
“¢ represents a hollow cylinder, the thin walls 
of which are bent backwards, the posterior part 
representing a longitudinal opening; for it is 
hollowed by a groove, termed the canal of the 
spinal marrow. This canal exists through the 
whole cylinder, and communicates with the - 
calamus scriptorius, with the fourth ventricle, 
which, strictly speaking, is but a dilatation of 
it. During the first periods we can, without 
difficulty, separate the thin and flexed walls of 
the spinal marrow, and thus expose the canal 
which they contain. This canal is somewhat 
broader in those points where the spinal marrow 
sensibly enlarges exteriorly, as at the origin of 
the nerves for the pectoral and abdominal ex- 
tremities. The mechanism of its formation is 
very simple: the pia mater, acquiring more 
extent, is folded longitudinally backwards and 
dips into the substance of the spinal marrow, 
which, as we have seen, had been previously 
in a fluid state. It is very evident that, in the 
commencement of the second, third, and even 
fourth months, this canal has, in proportion to 
the thickness of the walls of the spinal marrow, 
a much greater capacity than it subsequently 
acquires. The contraction which it undergoes 
in the progress of the developement of the 
embryo, arises from the pia mater depositing 
a new substance, the materials of which it 
derives from the blood sent by the heart, and 
which, augmenting the volume of the walls of 
the cylinder, ought necessarily to diminish the 
calibre of the central canal. This substance is 
soft, reddish, and traversed by numerous small 
vessels during the period of the last two 
months. We cannot doubt, then, that the 
grey substance of the spinal marrow has an 
origin subsequent to that of the medullary 
* Untersuchungen iiber die Textur des Riicken- 
marks. Leipz. 1842, 
