684 
space between them, and the central columns 
do not extend to the surface; and from the 
absence of any great developement of grey 
matter, we find no such arrangement as that 
which gives rise to the corpus dentatum in man. 
The olivary or central columns of the me- 
dulla oblongata pass into the mesocephale, 
occupying a plane superior to that of the py- 
smal fibres and of the transverse fibres. 
They may be traced upwards to the crus cerebri, 
where they seem to merge into the optic tha- 
lami, and to form a connection with the corpora 
uadrigemina posteriorly. 
, Ron's iaene are a distinctly in their 
ascent to the brain in the fourth ventricle, as 
two cylindrical columns (A, F, fig. 386). They 
form the floor of that cavity and are separated 
from each other by the longitudinal fissure 
which is continued upwards from the posterior 
fissure of the medulla oblongata. 
In the fourth ventricle the olivary columns 
are crossed by the fibres of origin of the 
portio mollis of the seventh pair of nerves, 
the white colour of which in the recent speci- 
men contrasts strikingly with the greyish hue 
of the columns themselves. We here see dis- 
tinctly that these columns are the source of 
origin of these nerves, and no doubt they are 
equally so of all the nerves which are con- 
nected with the medulla oblongata, namely, 
the fifth pair, the eighth, the ninth, and pro- 
bably also of the sixth. : 
The relation of the olivary columns in 
their upward course, to the other constituents 
of the mesocephale and crura cerebri, may 
be conveniently demonstrated in examining 
tranverse sections of those parts. We shall, 
therefore, return to this subject in descri- 
bing the anatomy of those portions of the 
brain. 
The following interpretation of the various 
columns of the medulla oblongata, referred to 
in the preceding description, has much foun- 
dation in their anatomical relations. 
The olivary or central columns constitute the 
fundamental of the medulla oblongata ; 
that, on which its action as a distinct and in- 
dependent centre depends, and in which the 
proper nerves of this segment of the ence- 
phalon are implanted. The continuity of those 
columns with the optic thalami and corpora 
uadrigemina materially enhances their phy- 
siological influence, and denotes their intimate 
association with some of the most important 
functions of the brain. And it may be added, 
that this connection of the medulla oblongata 
with which are ordinarily described as 
pertaining to the brain itself, shews that the 
original application of the term by Willis and 
Vieussens to a much greater extent of the en- 
cephalon is certainly more consistent with the 
physiological anatomy than that which is now 
employed for the convenience of description. 
There can be no doubt that the extent of this 
central and fundamental portion of the nervous 
system is limited above by the optic thalami 
and below by the spinal cord. 
The anterior pyramids connect the cerebral 
hemispheres with the spinal cord, the prin- 
NERVOUS SYSTEM. (Nervous Centres. Tue Encepmaton.) 4 
F 
cipal bundles of fibres decussating each other 
on the middle line, so that the right pyre 
is the medium of connection by the g 
number of its fibres between the right hemi 
sphere of the brain and the left half of the cord, 
but by a much smaller number between that 
same hemisphere and the right half of th 
cord. And so also of the left, mutatis mu= 
tandis. [tis highly probable too that the anteric 
pyramids derive fibres from the locus niger ¢ 
the crus cerebri and the vesicular matter of t 
mesocephale. These fibres, therefore, connec 
those segments with the spinal cord, but whe 
ther they contribute to the formation of th 
decussating or non-decussating bundles, or | 
that of both, it is impossible to determine, 
The restiform es ane evidently the con. 
necting fibres between the hemispheres of the 
cerebellum and the posterior and antero-lateral 
columns of the spinal cord. And the pos- 
terior pyramids connect the beg a? part of 
the medulla oblongata with the cervical and 
dorsal regions of the cord. 
Nerves—Numerous nerves are connectet 
with the medulla oblongata—a fact whie 
serves greatly to enhance its importance as_ 
centre of nervous action. These nerves are thi 
sixth pair, which are connected with the ante- 
rior pyramids just behind the posterior bordel 
of the pons; the ninth pair, or hypogloss 
nerves, which emerge along the anterior borde 
of the olivary body ; the seventh pair (portio 
mollis and portio dura), which emerge just b 
hind the upper extremity of the olivary body 
and the eighth ir, which arise alog te DOS: 
terior margin of the olivary body. ; 
OF THE MESOCEPHALE. — 
and olivary columns may be readily traced, a 
already explained, from the medulla oblongati 
up to the cerebral hemispheres; the form 
becoming united chiefly with the corpora strial 
the latter with the optic thalami. ; 
In that part of their course which is interm 
diate to the medulla oblongata these columns 
become mingled with certain transverse fibre 
and with more or less of vesicular matter, an 
with them contribute to form a mass which i 
the connecting link between all the segments: 
the cerebellum, and may be com to a ra 
road station, at which several lines meet ¢ 
cross each other. This is the mesocephale 
mesencephale. The name was suggested 
Chaussier, inasmuch as it forms “ to a cert: 
extent the middle and central part of the ent 
pate organ, the bond which unites the seve 
undles of fibres which contribute to its f 
mation.” -. 
The mesocephale may be isolated from 
other segments by dividing the crura cere 
just beyond the anterior margin of the pons, a 
the crura cerebelli as they penetrate the 
mispheres, and the medulla oblongata ona: 
with the posterior edge of the pons. ec 
cerebri emerge from it in front: the medu 
oblongata is connected with its poste 
face : on either side it is prolonged into 
cerebelli. Its inferior surface, which 
convex and looks forwards, is composed ¢ 
thick layer of arched fibres which fort 
i 
—) 
e@ pyram dal 
