—— re ,—“‘ ee 
the substance of the thalamus. 
glionic structure of the mamillary bodies is 
_ unfavourable to this view, and renders it more 
_ probable that they are independent structures, 
_ exercising proper functions as nervous centres ; 
NERVOUS CENTRES. (Human Anatomy. Tuer EncepHaton.) 
epiphysis upon the crus cerebri; and in this 
sense it may be classed with the striated bodies 
and the quadrigeminal tubercles, which, with 
the thalami, form a series of gangliform masses, 
pen in pairs, one beyond the other. 
e geniculate bodies, although intimately 
connected with the optic thalami, appear to be 
distinct from them, But very similar in struc- 
ture. A section made into the thalamus through 
either of them shows a distinct line of demar- 
cation between them. ‘The optic tracts adhere 
to the lower surface of each thalamus by their 
inner margins, and when followed backwards 
are found to form a very evident connection 
with both the geniculate bodies. 
Corpora mamillaria.—These bodies may be 
conveniently noticed here, as forming part of 
the series of gangliform masses in connection 
with the brain. They are of a spherical shape, 
covered on the exterior by very pure white 
matter, which is apparently derived from the 
anterior pillars of the fornix. When cut into, 
they are found to consist of a mixture of vesi- 
cular and fibrous matter, surrounded by a thin 
cortex of the latter. Microscopic examination 
proves this structure of the interior substance 
to be of the same nature as that of ganglia, 
and to resemble the optic thalamus. 
The fibrous matter is connected, at the upper 
part of each body with the anterior pillar of 
the fornix, and on the outside with a fascicu- 
lus of fibres from the optic thalamus. It has 
been supposed that these two bundles are con- 
tinuous, and that the mamillary body results 
from a twisting of the anterior pillar of the 
fornix as it changes its direction to pass into 
But the gan- 
and the constancy of these bodies in, at least, 
_ the mammiferous series, increases this proba- 
bility. 
Of the commissures of the brain.—A large 
number of fibres connected with the hemi- 
spheres or the two gangliform bodies just de- 
scribed, seem to serve the purpose of connect- 
ing different parts, either on the same side of 
the mesial plane, or on opposite sides of it. 
Those on the same side constitute the longitu- 
dinal commissures ; those on opposite sides the 
transverse. 
Of the longitudinal commissures.—These are 
four in number. They all evidently belong to 
the same system of fibres, separated from each 
other lg developement of intermediate 
parts. at which is on the highest plane is 
the superior longitudinal commissure, which is 
the fibrous matter of the internal convolution. 
Internal and a little inferior to this is a se- 
cond, very small, band of fibres, longitudinal 
tract, (Vicq. d’Azyr,) which passes from be- 
fore backwards along the middle of the corpus 
callosum, parallel to the superior longitudinal 
commissure, from which it is separated only 
by the grey matter of the convolution. Both 
these commissures are separated by the corpus 
701 
callosum from a third, which takes a parallel 
course to them, namely, the fornix, which 
occupies a plane considerably inferior to both. 
External to this and separated from it by the 
ventricular projection of the optic thalamus, 
we find a fourth band, which passes parallel to 
the fornix: this is the tenia semicircularis. 
As these parts have been already described, 
it will be unnecessary to do much more at pre- 
sent than indicate the connections which they 
serve to maintain. 
1. The superior longitudinal commissure con- 
nects the convolutions of the inferior surface 
of the anterior lobe with the hippocampus 
major; and as its fibres pass above the corpus 
callosum they form connections with some of 
the other convolutions on the internal surface 
of the hemisphere (fig. 395). 
2. The longitudinal tracts of the corpus cal- 
losum may be traced from about the same region 
of the inferior surface of the anterior lobe as 
the preceding commissure, near the perforated 
space, and they pass backwards, winding over 
the posterior reflection of the corpus callosum 
to its inferior surface. 
3. The fornix* is, next to the corpus callo- 
sum, the most extensive of the cerebral commis- 
sures. That it consists of longitudinal fibres 
cannot be doubted. Although commonly de- 
scribed as a single structure united at the body 
of the fornix, and spreading backwards and 
forwards by its crura, it nevertheless isdistinetly 
divisible along the middle line into two per- 
fectly symmetrical portions. The adhesion of 
the transverse fibres of the corpus callosum on 
its upper surface, and of the terminal fibres of 
its posterior reflection on its inferior surface 
which form the lyra, is the principal bond of 
union of these two lateral halves of the fornix. 
The separation of its anterior pillars in 
front affords strong indication of its double 
form. These pillars pass downwards in a 
curved course, through the grey matter of 
the tuber cinereum, to the mamillary bodies, 
which are connected to the optic thalami by a 
bundle of fibres which may be easily traced 
into them. ‘This bundle is described by Reil 
as the root of the anterior pillar of the fornix. 
From the gangliform structure of the corpus 
mamillare, I prefer to regard this band asa 
medium of connection with the optic thalamus, 
and to trace the anterior pillars to the ma- 
millary body. 
The parts with which the fornix is connected 
in front are the optic thalami, the mamillary bo- 
dies, and the septum lucidum, which consists of 
fibres having the same physiological import as 
those of the corpus callosum, altered however in 
direction by the backward position of the anterior 
pillars, which adhere to the body of the fornix. 
The tuber cinereum and the grey matter which 
adheres to the lower half of the inner surface of 
each optic thalamus, are connected~with it ; 
* This commissure is called votite a trois piliers by 
the French, Trigone cérébrale, Chaussier: arise, 
cope Varsoerdes of the Greeks. Mr. Solly has given 
an excellent delineation of the fornix in his work 
on the brain, pl. ix. 
