Quantitative studies of mitoses in cerebral hemispheres of fetal rats.

In continuation of our study of 15-day fetal rat brain development, evidence was obtained of a single layer of mitoses, situated away from the ventricle at a mean depth of 75% of the thickness of the cell layer of cerebral hemispheres ('deep mitoses'). Their number is 17.9% of ventricular mitoses and their spindles are perpendicular to spindles of ventricular mitoses. Their distribution is not correlated with distribution of ventricular mitoses. The fate and destination of these deep mitotic cells is at present unknown; the possibility that they are mitoses of the capillaries has been discussed.