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NERVOUS CENTRES. (Human Anatomy. Tur Encepnaton.) 
misphere. Again, Nos. 2, on opposite sides, 
resemble each other so closely that their sym- 
metrical relation cannot be doubted. The like- 
ness, however, is impaired by slight fissures in 
the convolution on the left which do not exist in 
that on the right side. Nos. 3 and 3 evidently 
correspond, but that of the right side is the larger 
and more undulating. And it may here be 
remarked that this great developement of the 
convolution marked 3 on the right side affects 
materially the position, relations, and shape of 
those in its neighbourhood, by throwing them 
backwards or outwards and altering their 
form. Thus the position and shape of con- 
volution 4 seems evidently modified by the 
large posterior undulations of convolution 3. 
In the brain from which the figure was taken, 
the convolutions on the right side are evidently 
larger and more highly developed than those 
of the left. It does not appear that there is 
any constancy with respect to the relative size 
of the convolutions of the right and left side, 
sometimes one side predominating, sometimes 
the other; nor have we any clue to discover 
the cause of the difference between the two 
hemispheres, or the reason of the variation as 
regards predominance of size. 
In the imperfectly developed brains of the 
infant or young child, the convolutions are 
quite symmetrical. They are so likewise in 
idiots, or persons of very inferior intellect, 
and, as has been already stated, in some Negro 
brains. 
The following convolutions of the human 
brain are constant in their position, although 
they differ much in different brains in size 
and developement. 
Fig. 
697 
1. The internal convolution, or that of the 
corpus callosum, called by Foville convolution 
dourlet (processo cristato, Rolando). The 
principal portion of this convolution is above 
and parallel to the corpus callosum : in front it 
curves down parallel to the anterior reflection 
of the corpus callosum, as far as the locus per- 
foratus, connecting itself with some of the ante- 
rior conyvolutions. Behind it passes in a similar 
manner round the posterior reflexion, connecting 
itself with some of the posterior convolutions, 
and in the middle lobe forming the hippocam- 
pus major, the anterior extremity of which is 
situate immediately behind the fissure of Sylvius 
and locus perforatus. Its horizontal portion 
appears to be connected with some nearly ver- 
tical ones, which seem indeed to branch off 
from it. (Fig. 395, O.) 
This is the most constant and regular con- 
volution of the brain. It exhibits with its fel- 
low of the opposite side very exact symmetry. 
Its inferior or concave border is smooth and 
uninterrupted, and forms the superior boun- 
dary of a sulcus, which intervenes between it 
and the surface of the corpus callosum. It 
forms, to use Foville’s expression, a hem or 
selvage to the cortical layer of the cerebral 
hemisphere. The fibrous matter which is in- 
closed by the cortical layer of this convolu- 
tion consists of longitudinal fibres following 
the same general direction, a large number of 
them no doubt bending inwards into the cor- © 
tical layer. These fibres are evidently com- 
missural in their office, and will be referred to 
by-and-bye as constituting the superior longi- 
tudinal commissure. 
The free margin of this convolution varies in 
395. 
Internal surface of the left hemisphere of the brain, shewing the connections of the internal convolution and the 
band of longitudinal fibres by which it is formed (d’ourlet), 
C, C, co 
, fornix 3 c, su 
by the locus niger. 
rpus callosum; O, O, O, internal convolution ; 6, septum lucidum; a, anterior commissure ; 
perior layer of the crus cerebri; d, inferior layer of the same separated from the former 
The fibres of the internal convolution are seen in the middle lobe extending tothe hippocampus major. 
