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A layer of cerebrospinal fluid surrounds the developing brain of normal human fetuses. The layer was found to occupy 13 to 26% of the intracranial space. Convolutions appeared in the hemispheres while this layer was still present. Neither growth of the skull nor the appearance of cortical convolutions is secondary to pressure from growth of the brain into a confined cranial space.
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Lanman et al. (1958) studied this question.
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