ON THE BRAINS OF TWO IDIOTS OF EUROPEAN DESCENT. 
553 
is therefore defective, but unequally so in the two. It is scarcely possible to doubt that 
dissection would establish the fact of a coincident want of development in the corpora 
striata of these brains. 
In both these idiots also the cerebellum is, comparatively to the cerebrum, enor- 
mously developed. In the smaller brain, only one-third of it is covered by the cere- 
brum ; in the larger brain, the two parts reach back to exactly the same level ; in both, 
the laminae appear to be few, only twenty being distinguishable on the under surface of 
one hemisphere in each. 
The skull of the male idiot is thin, and appears to be much marked on its internal 
surface with the convolutions ; that of the female idiot is thicker, and not so much marked 
in that way. 
b. Assuming the accuracy of the dates assigned to the several models of foetal brains 
in the Museum at Guy’s, the effect would be to place the period at which the idiots’ 
cerebra reached their ultimate stage of evolution, at from one month to even six weeks 
later than that given in the preceding paper. But it is notoriously difficult to deter- 
mine the age of any given foetus. An examination of the entire series shows that, if 
the dates be correct, the cerebrum does not, either in size, or in the condition of deve- 
lopment of its convolutions, always attain exactly the same point at exactly the same 
period of intra-uterine life. 
The condition of the convolutions in these models confirms the history above given 
of the conversion of the intrusive convolution into the anterior ascending parietal ; for 
the change is traceable through a certain number of the foetal brains. It also supports 
the views expressed as to the early arrest of the evolution of the corpora striata, and 
of the special effect of this on the development of the frontal lobes; for, with certain 
fluctuations, the corpora striata, where shown in the models, are always larger than the 
optic thalami ; and the proportions of the frontal to the hinder regions of the cerebrum, 
as marked off by the fissures of Kolakdo, vary, from the first appearance of this fissure 
to the full term of development, between the ratios of 37 to 63 and 58 to 42. Lastly, 
these models show that idiot brains must grow a little after they have ceased to be 
further evolved ; for the convolutions, and indeed the cerebral hemispheres themselves, 
are broader and larger in the idiot 'brains than in the models of brains of equally for- 
ward convolutional development. It is certainly true that, taking the four idiots’ brains, 
viz. the two hereinbefore described and the two in the Museum at St. Bartholomew’s, 
their respective sizes and their degrees of evolution correspond ; but this does not dis- 
prove the occurrence of a growth in them after the cessation of development, an event 
shown to occur on other grounds. 
The model and drawings of the idiot’s brain at Guy’s also confirm all our previous 
notions ; and indeed it may be concluded that the idiotic condition is produced in all 
cases by conformable influences, affecting the cerebrum in slightly different degrees in 
different examples. 
