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THE ANTIQUITY OF MAN 
complex varies very widely. It is highly possible that 
these later changes of the foetal brain may represent the 
later stages in the evolution of the human brain. 
While the passage from the simian to the human stage 
of development has affected every lobe of the cerebrum 
and of the cerebellum, there is one part which has 
undergone a peculiar change, one which is often fore- 
180 
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Fig. 146. — Profile drawing of the brain cast from the skull of a young gorilla 
superimposed on a corresponding drawing of the cast from the Gibraltar 
skull. The Gibraltar cast exceeds that of the gorilla in all dimensions. 
shadowed to a slight degree in the anthropoid brain. 
The change concerns the lowest part of the frontal lobe 
— the inferior or third frontal convolution. The actual 
part concerned is marked on the gorilla brain in fig. 146 
by the letter A. In the human brain this part has grown 
and expanded to such an extent that it reaches right back 
to the stem of the fissure of Sylvius, forming the anterior 
boundary of the stem (fig. 145, A). The old lower 
boundary of the third frontal convolution (marked 
