Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Todd, Robert Bentley
696 NERVOUS SYSTEM. (Nervous Centres. The Encephalon.) 
one type. Of this, as M. Leuret suggests, the 
brain of the fox may be taken as the basis. 
The fissure of Sylvius is well marked in this 
brain ; it is bounded by a prominent convolu¬ 
tion, which encloses it above, below, and 
behind—thus forming a curve, the concavity of 
which is directed forwards and downwards. 
Above and behind this we find a second con¬ 
volution forming a similar curve and parallel to 
the first. It exhibits a slight undulation, and 
is marked by a short fissure—signs of ad¬ 
vancing complication. Still further back and 
upwards there is a third convolution, parallel 
and curved similarly to the second ; this bifur¬ 
cates at one point. Above all, near the 
summit of the hemisphere, a fourth is found 
disposed in the same curved manner, but ex¬ 
hibiting some sinuosities or undulations at its 
anterior portion. A fifth convolution exists on 
the inferior surface of the anterior lobe and 
rests upon the roof of the orbit. Leuret de¬ 
signates it the supra-orhitar convolution. The 
sixth convolution is of great extent ; the prin¬ 
cipal portion of it is found on the inner surface 
of each hemisphere above the corpus callosum ; 
in front it bends downwards and backwards to 
the fissure of Sylvius, and behind it extends to 
the middle lobe and forms the hippocampus 
major. This convolution exists in a high state 
of developement in the human brain, and has 
attracted very generally the attention of ana¬ 
tomists. Foville describes it by the name 
convolution d’ourlet. 
Such is the most simple arrangement of the 
convolutions. The complication of this takes 
place by undulations being formed in the con¬ 
volutions themselves, by a subdivision of them 
at certain situations, by the junction of neigh¬ 
bouring ones through smaller folds crossing the 
sulci between them, and in the highest classes 
by the addition of totally new convolutions. 
Animals, whose brains have nearly the same 
degree of developement as that of the fox, 
have exactly the same convolutions, differing, 
however, somewhat in point of size. This in¬ 
crease of size is denoted by undulations formed 
in the course of convolutions throughout more 
or less of their extent. The dog may be taken 
as an example. M. Leuret states that, in com¬ 
paring the brains of several dogs together, he 
found with all of them the same convolutions, 
differing only in the extent of undulations and 
the number of depressions, both of which were 
greatest in the largest brains. The brain of a 
large mastiff (chien dogue), a good watch-dog, 
of such great ferocity that he attacked the person 
who fed him, had all the convolutions very 
large and much undulated, with numerous 
depressions in them. 
A group of animals, consisting of the cats 
and the hyena, exhibits another stage of in¬ 
crease in the developement of convolutions. 
The same type prevails as in the fox and dog ; 
four external convolutions, one internal, and a 
supra-orbitar. These convolutions, however, 
are united to each other at numerous points by 
means of small folds crossing the sulci. These 
uniting folds form the secondary or supple¬ 
mentary convolutions. Nearly all the primary 
convolutions have supplementary ones con¬ 
nected with them. 
A group, which includes the sheep and other 
ruminant animals, exhibits much more com¬ 
plication in the cerebral convolutions, but still 
preserves the same type. The undulations 
and the supplementary convolutions are more 
numerous. The primary appear less nu¬ 
merous because less distinct. The anterior 
part of the internal convolution is much in¬ 
creased in developement, and the supra-orbitar 
is much more complex. In the fissure of 
Sylvius some small convolutions are found 
which are the first developement of those which 
in the human subject constitute the insula of 
In the brain of the elephant new convolu¬ 
tions are added. These consist of folds pass¬ 
ing in a perpendicular direction ; the primitive 
convolutions always taking a longitudinal 
course. These latter are divided by the former 
into an anterior and a posterior set. Others 
are found above and in front of the fissure of 
Sylvius ; three superior convolutions are found, 
the continuations of which backwards are 
situate above the internal convolution. All 
the convolutions of the elephant are remark¬ 
ably undulating and exhibit numerous depres¬ 
sions. The brain of the whale is very similar 
to it in this respect, and both resemble that of 
Monkeys have not the tortuous or com¬ 
plicated convolutions which are found in the 
whale and elephant. Yet the developement 
of the hemispheres at their posterior part, the 
general form of the brain, the extent and in¬ 
clination of the fissure of Sylvius approximate 
the brain of monkeys to that of man much 
more nearly than the whale’s or elephant’s, 
which, notwithstanding their complicated con¬ 
volutions, are generally inferior in organization, 
and resemble the brains of other Mammalia. 
The internal convolution in monkeys is simple ; 
below and behind it forms the hippocampus, 
from which convolutions are prolonged back¬ 
wards, forming the posterior lobe. Two supe¬ 
rior convolutions are met with above the fissure 
of Sylvius, between which is placed a trans¬ 
verse fissure very constant, called the fissure of 
Rolando. The orbitar convolutions are largely 
In comparing the human brain with that of 
the inferior animals, we notice great exactness 
of symmetry between the convolutions of op¬ 
posite hemispheres in the latter, and the want 
of it in the former. It cannot, however, be said 
that the convolutions of opposite hemispheres in 
the human subject are absolutely unsymmetri- 
cal. A careful examination will show that the 
same convolutions exist on each side, but appa¬ 
rently of different sizes, and not closely correspon¬ 
ding as regards situation. My meaning will be 
more readily understood by referring to fig. 
381, p. 671, where the same numbers have 
been affixed to corresponding convolutions. 
No. 1 on the right has a certain general re¬ 
semblance with No. 1 on the left, which would 
be much more perfect but for the fissure 
which marks the convolution of the right he-


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