The Fine Structure of the Subcommissural Organ of the Human Fetus

Abstract

The subcommissural organ of the human fetus of both sexes from 5 to 8 months of age was studied by electron microscopy with special attention to physiological significance.
The subcommissural organ consists of tall columnar ependymal cells with long basal processes. The apical surface of the ependymal cell facing the third ventricle is provided with a number of microvilli, few cilia and occasional cytoplasmic protrusions. No structure corresponding to Reissner's fiber could be seen in the ventricle. The cytoplasm of the ependymal cells, although its electron density varies considerably from cell to cell, contains a large number of glycogen granules, a moderate number of mitochondria, a relatively well-developed Golgi complex, and bundles of microtubules running parallel to each other. The granular endoplasmic reticulum is scantily scattered in a tubular form in the cytoplasm except for the basal portion where the endoplasmic reticulum is frequently arranged in a concentric array.
In the subcommissural ependymal cells of the human fetuses examined, neither secretory sacs filled with the fine flocculent material characteristic of this organ in other species nor any morphological evidence for secretory activity in this organ could be detected. The results may indicate that in human beings the subcommissural organ is not secretory in nature, buy rudimentary.