The posterior horn and collateral trigone of the lateral ventricle of the monkey brain (Macaca speziosa). A scanning electron microscopic study.

The posterior horn of the lateral ventricle in the monkey brain varies in size in different individuals. In this part of the ventricle, the ependymal cells bear cilia, microvilli, microblebs and supraependymal, axon-like cell processes. Only slight differences are seen in the different parts of the posterior horn: The roof has densely packed cilia and microvilli. Supraependymal axons are almost absent. The lateral wall has axons which are irregularly arranged. Subependymal vessels are partly covered by polygonal ependymal cells. The collateral trigone has some regions with densely packed cilia and some with widely spaced cilia. The regions with widely spaced cilia have polygonal cells whose surfaces differ in shape and are surrounded by a border of microvilli. The meshwork of supraependymal axons is wide-spread on polygonal cells. The medial wall shows no regional differences. Though larger areas are free of supraependymal cell processes, all ependymal structures (cilia, microvilli, microblebs) are present. In the posterior horn of only two animals were these larger spherical protrusions present which could be the result of a secretory process.