ON THE BRAINS OE TWO IDIOTS OE EUROPEAN DESCENT. 
543 
In the two foetal brains represented by Leuret and Gratiolet, already alluded to, the 
parts in front of the fissure of Rolando, comprising the frontal lobe and the so-called 
anterior ascending parietal convolution (which latter should, I think, be associated 
with the frontal region itself), form a far larger proportion of the entire cerebrum than 
they do in the idiots’ brains. In the brain of the human foetus between the fourth and 
fifth months (Plate XXIII. figs. 21 & 22), in which the fissure of Rolando ( d - d ), the 
great parallel temporal fissure (/), and the perpendicular fissure (h) are clearly traceable, 
the same fact is well illustrated. In foetal brains at still earlier periods* the same thing 
is observable, whilst at later periods than the seventh month the parts in front of the 
fissure of Rolando become still longer in proportion to those behind it. Indeed, in the 
normal course of development, there is no period at which the frontal part seems, as it 
were, to stand still, or retrograde relatively to the rest of the cerebrum ; but after once the 
fissure of Rolando is formed, there is a variable but progressive relative increase of the 
parts in front of that fissure. It is certain, therefore, that the frontal lobes of the idiots’ 
cerebra are not proportionally developed in comparison with the temporo-parietal regions. 
The same appears to me to be true likewise of the occipital lobe ; but we may confine 
the argument here to the defective state of the frontal lobes. 
Fully to appreciate the importance of the diminutive size of these last-named lobes, 
we must take into account certain facts to be hereafter stated in detail, regarding the 
internal structure of the cerebral hemispheres. The corpora striata in the idiots’ brains 
are very small ; not merely absolutely, but also relatively to the size of the optic thalami, 
the ordinary proportions between these two ganglia being actually reversed, the former 
being usually much larger than the latter, whilst in the idiots’ brains they are much 
smaller. Since in a series of normally developed foetuses the corpora striata, at all 
periods, form larger masses than the optic thalami, we have further evidence, within the 
idiots’ brains themselves, of the fact already announced of an irregular and dispropor- 
tionate development of their parts. There is, indeed, an obvious correspondence between 
the diminutive size of the corpora striata and that of the frontal lobes; whilst the 
relatively larger optic thalami are associated with a larger growth of the hinder portion, 
especially of the temporo-parietal regions. 
The conclusions which we would draw from the preceding facts are these : — First. 
Instead of the idiots’ cerebra having been uniformly and normally developed up to a 
certain date (say the latter part of the seventh month), and having then been subjected 
to a general cessation of development, they have experienced an inequality or irregu- 
larity of evolution in certain of their parts. Secondly. Whilst all parts have been more 
or less arrested, the frontal and occipital lobes have suffered more than the temporal 
and parietal. Thirdly. Whilst both the large ganglia at the base of the cerebrum 
(those cores or nuclei of the cerebral hemispheres, the corpora striata and optic thalami) 
have participated in this disturbance of the ordinary course and degree of evolution, 
* See Leuret, loc. cit. pi. 29, from fig. 10 ; and also Tiedemajvn, Anat. Bildungsgeschichte des Gehirns. 
Niimberg, 1816. 
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