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Foetal brain. Coronal (top) view of the brain of a 24-week-old foetus, the front of the brain is at top. Although at this stage of development the foetal brain shows active auditory and visual responses, it is yet to develop the characteristic folds. A groove (sulcus, down centre) separates the two cerebral hemispheres. (KEYSTONE/SCIENCE PHOTO LIBRARY/DR G. MOSCOSO)