4 
ub 
i’ 
j 
___ The direction of the long axis of the third 
ventricle is obliquely downwards and back- 
wards. Its anterior extremity being on a 
higher plane than its posterior, is therefore 
_ likewise superior. 
Pineal gland—We may here conveniently 
_ hotice the position and connections of the 
' pineal gland. This body, rendered famous by 
_ the vague theory of Des Cartes, which viewed 
it as the chief source of nervous power, is 
_ Placed just behind the third ventricle, resting 
‘in a superficial groove which passes along the 
_ Median line between the corpora quadrige- 
if mina. It is heart-shaped, and of a grey co- 
Tour. Its apex is directed backwards and 
downwards, and its base forwards and up- 
wards. A process from the deep layer of the 
‘lum interpositum envelopes it and serves to 
in it in its place. From each angle of its 
These processes serve to con-: 
“nect the pineal body to the optic thalami. 
they are called the peduncles of the pineal 
land, also hubene. In general they are two 
im number, one for each optic thalamus. They 
may be traced forwards as far as the anterior 
lars of the fornix. Posteriorly these pro- 
ses are connected along the median line by 
ome white fibres which adhere to the base 
the pineal gland, as well as to the posterior 
amissure beneath, and which seem to 
m part of the system of fibres belonging to 
that commissure. A pair of small bands 
‘Sometimes pass off from these fibres, along 
Optic thalami, parallel to the peduncles 
ve described. 
___Itappears, then, that the pineal gland has no 
er connexion with the brain than that which 
e habene or peduncles secure for it ; other- 
this body might more appropriately be 
egarded as an appendage to the pia mater, in 
ich it is involved, and from which it derives 
trition. 
ted with the internal processes of the pia 
ter, are found in the pineal body ina large 
“proportion of instances in the adult. They 
han. be accumulated as it were in a cavity 
is situate towards its base. Hence So- 
“emmering gave to this collection of sabulous 
ae we name acervulus. When, however, 
the sand is abundant, it may be found upon 
the: as well as in the centre. 
_ the anterior commissure. —In examining 
the third ventricle, a rounded cord of very pure 
white. matter is seen through the interval which 
is isi.by the divergence of the anterior pillars 
| of the fornix in their descent to the base of the 
| brain. This band is transverse, and a pears 
| to form a tangent to the convex border of 
those pillars. It may be traced outwards on 
. either side through the anterior extremities of the 
} Co striata into the white substance of the 
middle lobes of the brain. A very little dis- 
Section is required to expose this cord in its 
entire extent. It seems placed in a canal hol- 
lowed in the cerebral matter. When exposed, 
i 
NERVOUS CENTRES. (Human Anatomy. Tne Encepaton.) 
7 
677 
its surface is perfectly smooth, indicating that 
fibres do not pass from it to the wall of the 
canal in which it lies. Examined in its whole 
extent, it presents the form of a curve with an- 
terior convexity, and becomes gradually flat- 
tened and expanded towards each extremity, 
its component fibres becoming divergent and 
mingling with the white substance of that por- 
tion of the brain. 
This system of fibres possesses the characters 
of a commissure or bond of connection between 
symmetrical portions of the brain on either side 
of the median plane as distinctly as the corpus 
callosum itself. 
The soft commissure.—The cavity of the 
third ventricle is partly occupied by a lamina 
of a light grey matter, which extends between 
the optic thalami of opposite sides. It forms a 
transverse horizontal plane dividing the ven- 
tricle into two portions, one above, the other 
below it. Sometimes it is divided and disposed 
as two planes. There is but little power of cohe- 
sion between its particles, so that in the recent 
state the separation of the thalami in the neces- 
sary manipulations will frequently cause its 
rupture. Hence the adjunct “ soft”? is appro- 
priately applied to it, and by its connecting the 
thalami of opposite sides, this structure may be 
ranked with the other commissures. It does 
not extend throughout the entire length of the 
ventricle: both its anterior and posterior mar- 
gins are concave and leave an open space be- 
tween each extremity of the ventricle. 
Thus far our examination includes the topo- 
graphical anatomy of the cerebrum proper. 
The pineal body, indeed, scarcely lies within 
the confines of that segment of the encephalon, 
but from its internal relation to the third ven- 
tricle and the optic thalami, it must be included 
in the description of those parts. This body 
rests on the upper surface of that segment of 
the brain which lies intermediate to the ce- 
rebroum, cerebellum, and medulla oblongata, 
namely, the mesocephale. And we shall now 
proceed to a brief notice of this part and its 
connection to the other segments. 
The mesocephale—F our eminences are seen 
immediately behind the third ventricle. A 
transverse furrow separates them into an 
anterior and a posterior pair, and a longitudinal 
furrow along the median line divides the 
right and left pair from each other. The pineal 
body rests in the anterior extremity of the lon- 
gitudinal depression. The anterior pair have 
been long named the na/es, the posterior the 
testes. In the human subject the former are 
the larger. In the inferior mammalia these 
bodies are much more highly developed than 
in man, and exhibit a more marked difference 
of size. : 
The posterior of the corpora quadrigemina 
are apparently connected to the cerebellum by 
two columns of white matter, one of, which 
passes into the central white substance of each 
cerebellar hemisphere. These are the processus 
cerebelli ad testes. They enter into the for- 
mation of the crura cerebelli. Each of them 
forms the superior layer of the crus cerebelli of 
its own side. 
