A localised growth zone in the wall of the developing mouse telencephalon.

In sections of the prenatal mouse brain, sites of maximum area increase of the lateral ventricle were mapped onto reconstructions of the ventricular surface. This was done by identifying areas of ventricular layer where mitotic density was high and the adjacent intermediate layer either absent or thinly populated with neurons. It was assumed that in these areas, cell division was producing ventricular cells rather than neurons and that they were therefore gaining in area, whereas sites against which neurons were accumulating were either ceasing to increase in area or at least were increasing more slowly. Such an area occupied a zone at the junction between the medial and lateral telencephalic walls. The zone was eliminated during development in a rostrocaudal direction. It is suggested that modulation of growth along this zone may be an important factor in fashioning the form of the ventricular cavity.