The floor of the fourth ventricle in the perinatal period in humans: new morphological findings.

The floor of the fourth ventricle is generally believed to show basically adult morphological characteristics in man by the perinatal period. This descriptive study and statistical analysis of 163 brainstems from human fetuses and neonates demonstrates that in this period, the floor of the fourth ventricle presents a series of folds and grooves of variable size and sequence, which during the perinatal period clearly increase the surface area of the germinal layer overlying them. These features are not seen in adults.