698 
its characters in different brains, according to 
the of tortuosity it exhibits, and the 
number of small fissures which are met with in 
it. The small folds which connect it with other 
conyolutions on the inner surface of the hemi- 
sphere vary in number, and are generally found 
most numerous at its posterior me of 
these folds are not distinctly visible unless the 
sulcus above it has been freely opened, as they 
are situated quite on its floor. 
2. The convolution of the Sylvian fissure — 
This convolution forms the immediate boun- 
dary of this great fissure. We have seen its 
early developement in the simple brain of the 
fox, and we may observe it gradually rising in 
complexity through all the intermediate stages 
up to the most highly developed brains. In 
the elephant it is remarkably tortuous, and is 
connected anteriorly as well as posteriorly with 
convolutions which pass to the anterior and su- 
rior and to the posterior part of the brain.* 
nh man it is also very tortuous, and the nume- 
rous folds which pass from it forwards or back- 
wards, forming primary or secondary convolu- 
tions, render it Fificult to isolate it sufficiently 
for the anatomist to follow it throughout its entire 
course. Its inner border is likewise interrupted 
by the connections which it forms with the con- 
volutions of the floor of the Sylvian fissure. 
3. Within the fissure of Sylvius we find that 
remarkable group of convolutions called by Reil 
insula, the island. It consists of a series of 
small folds radiating from a common centre and 
connected with the convolution last described 
by still smaller folds, which cannot be seen 
unless when the fissure has been very freely laid 
open. The centre from which the convolutions 
radiate is the apex of a cone, the base of which 
adheres to the floor of the fissure. 
4. On the inferior surface of the anterior 
lobe there is a pair of longitudinal convolutions 
which enclose between them the fissure of the 
olfactory process. The external of these con- 
volutions is continuous with the convolution of 
the Sylvian fissure. 
The numerous secondary convolutions which 
are found over the surfaces of the brain render 
it difficult to distinguish the primary ones. 
These latter are indicated hy the antero-poste- 
rior course which they take—the former being 
more or less vertical. The largest and most 
tortuous convolutions are found on that part of 
the external surface which corresponds to the 
parietal bone. Next to them, in point of size, 
‘ are the convolutions of the anterior lobe, but 
the smallest of all are those of the posterior 
lobes. 
The hippocampi, major and minor, are 
constant convolutions, which project into the 
lateral ventricles, the latter into its posterior, 
the former into its descending horn. 
In general the constituent fibres of the white 
matter of the convolutions converge from the 
inner surface of the cortical layer to the cen- 
trum ovale, or if followed from the centrum 
ovale, they radiate to the grey surface, whether 
* See Leuret, pl. xiv. representing the external 
surface of the elephant’s brain. 
NERVOUS SYSTEM. (Nervous Cenrres. Tur Encepnaron.) : 
of a convolution or of a suleus. A remarkabl 
exception is in the case of the internal cony 
glade fibrous prac Rea g constitutes, 
as has been already explai a itudin 
commissure. The thickness ‘of a cortica 
layer is pretty uniform, at least relatively te 
the size of the folds themselves. Throughou 
its entire thickness it is mixed with fibres, whie 
are most numerous at its adherent sur 
but extremely few and scattered at its fix 
surface. _p 
In hydrocephalus the convolutions disap 
pear. The fibrous matter becomes e 
panded by the fluid accumulated in the vei 
tricles, and when its expansion has gone so 
as to equal the grey surface, the folded cha= 
racter of the latter disappears. This take 
place precisely in the same way that the rug 
of the contracted stomach (as before referred te 
become obliterated when muscular coat rm 
laxes and allows the full distension of the org a 
Mayo supposes that other fibres are found 
the convolutions besides those which are ce 
nued into the centrum ovale. These are con 
missural ones, which pass from convolution | 
convolution—either between adjacent or dis 
tant ones—forming arches the convexities 
which are directed to the centrum ovale. — 
have never succeeded in satisfying myself ¢ 
the existence of such fibres either in the fin 
brain or in that preserved in spirit. If the 
exist, it is evident that they must be commi: 
sural between particular convolutions. T 
same anatomist supposes that similar com 
sural fibres connect the lamine of the 
bellum. 
The principal bulk of the hemispheres 
formed by fibrous substance. This is shor 
by the horizontal section which displays 
centrum ovale. These fibres radiate from th 
surfaces of the optic thalami and corpora striz 
which are in contact with the substance of t 
hemisphere. Most of the fibres which emer 
from these gangliform bodies to the gi 
matter of the convolutions, me, howeve 
turn inwards towards the mesial 
form the corpus callosum by their union ¥ 
those of the opposite side. , 
It cannot be supposed that all the rema 
fibres, after subtracting those which forr 
corpus callosum, through halami ; 
corpora striata. The dispenoaian of num 
between the fibres of the medulla oblong 
and these is too striking to allow such an 
pothesis, They mingle with the vesicular 
ter of both; some do not pase beyonaa 
others are continued into the ulla © 
gata, either to its olivary or its pyramid 
ne 
orpora striata and optic thalami.— 
corpora striata and optic thalashi beara s 
resemblance in general character and stru 
to ganglia. They are ovoid masses place 
tween the fibrous substance of the hemisp 
on the one hand, and the medulla oblongati 
the other. These bodies, which are best 
played by laying open the lateral ventr 
(p- 675), are very closely united to each 
The corpus striatum is placed a little in fi 
ie 
i 
Saye 
