546 PROFESSOR MARSHALL ON THE BRAIN OF A BTTSHWOMAN; AND 
connecting convolution, and the absence of the upper one ; and lastly, the great breadth 
of the connecting ridge which joins the callosal and uncinate convolutions. 
Although, therefore, so defective in developmental detail, these microcephalic cerebra 
are still human, and differ as much from the Ape’s cerebrum, or constitute as little an 
intermediate step towards it, as any other bodily defect in man is found to differ from 
a truly quadrumanous form, or manifest a serial approximation to it. Just as in a case 
of webbed human fingers the digits are still human and not gorilla-like, and just as in 
the deformity named talipes valgus, though the foot is inverted and the weight of the 
body is supported on its outer border, still the member is human and not ape-like, so 
these brains, though simplified by defect, possess characteristics which distinguish them 
as imperfectly human yet not quadrumanous. The community of plan observable in 
the brains of all the Primates, including Man himself, necessitates a general conformity 
to that plan, even in these defective human brains ; but the special marks of human 
divergence from that plan have already been set upon them at some very early, probably 
at the earliest moment of their development. 
e. Internal Structure of the Idiots’ Cerebra and Cerebella, The Commissures , 
Cavities , Ganglionic Masses, and Laminae. 
Excluding the great fissures, the depth of the sulci (or, in other words, the prominence 
of the convolutions) in the idiots’ brains is greatest in the lateral temporal region, next 
in the frontal and parietal regions, and least in the occipital region, where many of the 
sulci are mere marks or notches. The average depth of the sulci is, in the idiot woman’s 
brain, - 5 inch, in the idiot boy’s '4 inch. In the idiot boy the thickness of the grey 
matter in the recent brain varied between -^ths and ^ths of an inch ; in the preserved 
brain it varies from -g^-ths to - 3 %ths of an inch, averaging - 3 %ths. In the idiot woman it 
ranges between -^-ths and g^-ths, averaging about -^ths ; in both brains it is, as usual, 
thickest in the frontal and parietal regions, and thinnest in the occipital. Unlike what 
is found in the Chimpanzee’s brain, the quantity of white matter in proportion to the 
grey is very large, in accordance, as we shall find, with the relatively full development 
of the transverse commissural system of fibres. 
The corpus callosum, in both the idiots’ brains, is proportionally shorter though thicker 
than in the perfect human brain, but it is relatively longer than in the Chimpanzee. In 
the recent brain of the idiot boy it measures '75 inch long. Its length, greatest thickness, 
least thickness, and average thickness in the preserved brain of the idiot woman are 
46, 13, 6, and 7 thirtieths of an inch; in the idiot boy 41, 7, 4, and 5 thirtieths of an 
inch. The sectional area of this part in the idiot woman is about §-Q-§ths of an inch, 
in the idiot boy only fifths of an inch. Comparing these numbers with the area of 
the internal surface of one cerebral hemisphere, we find that in the idiot woman the 
ratio is as 1 to 18-3, in the idiot boy as 1 to 14*5, whereas in the perfect human brain 
the ratio is 1 to 12*5, and in the Ape as 1 to 28*5 ; so that in respect of the transverse 
commissural fibres of the corpus callosum, the idiots’ brains, diminutive as they are, are 
truly human in their structure. The anterior and posterior commissures likewise are 
r 
