ON THE BRAINS OE TWO IDIOTS OE EUROPEAN DESCENT. 
539 
and lowest external connecting convolutions, though broad and superficial (the second 
being especially massive), are so simple, in comparison with their singular complexity 
and extraordinary tortuosity in the perfect brain, as to form mere bands between the 
temporal and occipital lobes. Nevertheless this part of the brain, more deeply furrowed 
in the woman than in the boy, but larger from before backwards in the boy than in the 
woman, is relatively well developed, and has perfectly human characters ; for all four 
connecting convolutions exist, instead of there being defects in one or other of the two 
upper ones, as is found in the higher Apes. They are also, as seen above, singularly 
asymmetrical. 
On the inner surface of the hemisphere the marginal convolution (Plates XXI. % 
& XXII. figs. 13 & 17, 17 - 17 ) pursues its usual course, and terminates just behind the 
upper ends of the two ascending parietal convolutions. Like these convolutions, and 
owing also to a defective development backwards of the frontal lobe, it does not extend 
so far back as in the perfect brain, but, becoming very narrow, stops, in the idiot woman, 
on the left side (Plate XXI. fig. 13) at a point opposite the hinder border of the corpus 
callosum ( c ), on the right side somewhat short of that point. In the idiot boy (Plate 
XXII. fig. 17) it is on both sides arrested at a point a little in front of the hinder border 
of the corpus callosum. In the idiot woman, instead of the numerous radiating secondary 
sulci which in the perfect state cut up this convolution into little quadrangular lobes, 
only two or three such sulci exist, passing horizontally forwards in front of the corpus 
callosum ; below the anterior border of the corpus callosum is another rudimentary lon- 
gitudinal sulcus, and a little depression indicative of a second ; above the corpus callo- 
sum this marginal convolution is joined, as usual (#), to the convolution of the corpus 
callosum (is— is), and then becomes very wide, and faintly marked with a slight depres- 
sion. In the idiot boy’s brain the same description would suffice. In both brains its 
forms and subdivisions, simple as they are, imitate closely its general features in the per- 
fect state, but are wanting in complexity. As compared with its condition in the Apes, 
it is less uniform in width, and far less frequently subdivided by secondary sulci. 
The convolution of the corpus callosum (Plates XXI. & XXII. figs. 13 & 17, is-is) occu- 
pies its customary position around that commissure, but differs from its condition in the 
perfect brain by the absolute smoothness of its surface and the absence of the peculiar 
crest-like upper margin posteriorly. It is equally smooth in both the idiots’ brains. Its 
surface is more complex in the higher Apes. In the idiots’ brains the marginal convo- 
lution ( 17 ) greatly exceeds in width the subjacent convolution of the corpus callosum (is), 
especially in the region in front of and below the corpus callosum — a character well 
marked also in the perfect European brain — whereas in the Ape the proportionate space 
occupied by the two convolutions is nearly equal. The connecting bridge of convolu- 
tional substance (#) passing from one to the other in both the idiots’ brains, on both 
hemispheres, is usually present also in the human brain, but not in the brains of the 
higher Apes. 
The guadrilateral lobule in both the idiots’ brains (Plates XXI. & XXII. figs. 13 
