OX THE BRAINS OF TWO IDIOTS OF EUROPEAN DESCENT. 
53B 
fissure (Plates XXI. & XXII. figs. 13 & 17, i-i), in the idiot woman, curves as usual 
around the corpus callosum, but sooner reaches the upper border of the hemisphere, 
a little short of the hinder margin of that commissure. It is interrupted, as usual, by a 
convolution (#) just above the front of the corpus callosum. In the idiot boy’s brain this 
fissure has a similar course, and is also interrupted (#) immediately in front of the corpus 
callosum ; but it reaches the upper border of the hemisphere opposite the hinder end 
of the corpus callosum. This fissure is nearly symmetrical, in both idiots, on the two 
sides. 
The internal perpendicular fissure (h) in the idiot woman is short and simple, and 
inclines backwards from a point about half an inch behind the corpus callosum ; it 
joins the fissure of the hippocampi below, but a rudimentary connecting convolution 
exists in this situation. In the idiot boy this fissure has precisely the same arrange- 
ment. 
The fissure of the hippocampi (Plates XXI. & XXII. figs. 13 & 17, l-l, m), in both 
brains, is less horizontal than usual. In the idiot woman its calcarine portion (fig. 13, l) 
terminates on the very point of the occipital lobe, in an open notch. On the right 
hemisphere, its anterior portion passes, as usual, a short distance beneath the cerebral 
peduncle ; but on the left side it curves outwards on the under surface of the temporal 
lobe, and joins a deep sulcus which represents an irregular collateral fissure. In the idiot 
boy, on the left side, the fissure of the hippocampi is simple in outline and oblique in 
direction, reaches the tip of the occipital lobe, and extends forwards to the side of the 
cerebral peduncle. On the right side this fissure is represented by two deep parallel 
sulci (fig. 17, l-l), separated by a thin ridge ( 26 ) of convolutional substance. A further 
development of the convolutions above and below would have concealed this ridge, and 
left a single fissure. 
The collateral fissure (Plate XXII. fig. 17, n-n) is normal but simple in both idiots, 
except, as above alluded to, on the left hemisphere in the idiot woman. 
On comparing the fissures of the idiots’ brains with those of the healthy human brain 
on the one hand, and those of the Chimpanzee on the other, the following points deserve 
notice. The Sylvian fissure is both shorter and much more vertical in the idiots’ than in 
either the human or quadrumanous brain, owing evidently to the defective development 
of the fronto-parietal region of the cerebrum in its ordinary backward direction, and 
to the disproportionate size of the temporal region. In respect to the former region, 
the idiots’ brains manifest a marked inferiority even to the Ape ; for, whilst the masses of 
brain seen on the lateral aspect in the Chimpanzee, in front of and behind the Sylvian 
fissure, appear nearly equal, or even show a preponderance in front, in the idiots’ brains 
the quantity in front is only about half the quantity behind. In the healthy human 
brain, the preponderance is decidedly in the fronto-parietal region. The fissure of 
Rolando, so complex and zigzag in the healthy human brain, is in the idiots’ brains, 
even on the side where it is most clearly traceable, a simple oblique sulcus, a little 
curved at its outer end, where, like the Sylvian fissure, and for the same reason, it is 
mdccclxiv. 4 B 
