2 8 O B S E R V A T I O N S ON T H E
C H A P T E R IX.
Of the Strudure of the Spinal Marrow.
T .
I^ H E fpinal marrow, like the nerves of the head, feems to derive its origin
from, or to be a continuation of the medullary fubftances of
the brain and cerebellum, and may be confidered as the largeft nerve of the
body. We iliall find that it is divided, behind as well as before, to a greatr
er depth than we would fuppofe from the defcriptions given by late writers,
fo as to be compofed of two cords, joined together at their middle or deepeft
parts by a lamella, which confifts chiefly of red veflels and cineritious
matter
Nay, when either of thefe two cords is accurately examined, it will be
found to be fubdivided by a flight furrow, into a fmall pofl:erior cord and
large anterior cord. In the former, fafcicuU of longitudinal fibres readily
appear; in the latter, the difpofition of the medullary fibres is much lefs evident.
In the medulla oblongata, confiderable vefliels pafs from the anterior rima
or calamus fcriptorius to the pollerior fiiTure; and hence the two cords feem
to be joined by tranfverfe fafciculi of the medullary fibres f ; but in the
fpinal marrow thefe veiTels are fmall, and the joining of the two principal
cords feems to be made by a thick plate of cineritious fubfl:ance. When
we cut the fpinal marrow tranfvcrfely, the internal cineritious fubfl:ance
makes
• See Tab. VII. Fig. 2. And Tab. IX. Fig. 4. 5. 6. 7. 8.
t See Tab. V. And Tab. VU. M. N. O.
N E R V O U S S Y S T E M . 2 9
makes a cruciform appearance, or confifts of four portions, one correfponding
to each of the four cords of which I have obferved it confifts *.
The furface of the fpinal marrow, which is covered with the pia mater,
has been defcribcd as a pure medullary fubftance f ; but, although it has a
great deal of the medullary matter in it, yet if, in a recent large animal, as
the ox, a tranfverfe fedUon be carefully examined, the outer layer will be
found to contain a confiderable quantity of cineritious matter, or the fpinal
marrow alfo will be found to have cineritious cortical matter under its pia
mater, and, in general, to agree with the brain in its ftruilure.
S T . II.
BETWEEN the anterior and pofterior bundles of fibres which form the fpinal
nerves, a ligament is conneiled, by a number of threads, to each fide of
the pia mater of the fpinal marrow, through its whole length, for its fupport,"
of which, as no fufficiently accurate defcription or figure has been
given, I have had a drawing made J . As this ligament is fixed, by a number
of teeth, to tlie inner fide of the iheath, formed by the dura mater, it has
been called Denticulatum. The greater number of thefe teeth run tranfvcrfely,
fome afcend, others defcend ||, all fplit into fibres, which are incorporated
with the fibres of the inner layer of the dura mater. From the
conical under end of the fpinal marrow, a cord is produced which reaches
to the 03 coccygis, and there fplits into threads, which may be confidered
as the termination of the laft teeth of the ligamentum denticulatum.
H SE C T .
• The cruciform appearance of the cineritious fubftance of the fpinal marrow was known to Blafius
and a few other writen, as Huber, &c.; but as they did not remark, that each fide of the fpinal marrow
is fubdivided into two c'olumns, the caufe of tlie cruciform appearance was not underftood by
them.
t Natura mcdullae fpinalis eft, quam vox declarat, medullaris omnino, maitima certe parte fui, et
externa tot a facie.
I See Tab. X. Fig. i.
II See Tab. X. Fig. i. a. b. x.
• • See Tab. X. Fig. w. x.