A scanning electron microscope study of the pineal recess of the adult brush-tailed possum (Trichosurus vulpecula).

The ventricular surface features of the pineal recess of 35 adult brush-tailed possums (Trichosurus vulpecula) were studied, mainly with the scanning microscope. The complex and interesting details observed have not been reported before. The pineal recess shows three distinct zones, and it is suggested that these be called: central, paracentral, and peripheral. The surface cells of the central zone show neither cilia nor microvilli, the paracentral zone shows microvilli (in a polygonal and homogeneous array), supraependymal cells and CSF-contacting nerve processes, while the peripheral zone is heavily ciliated. These features are consistent with the hypothesis that, in certain physiological states, the CSF from the pineal recess carrying pineal secretion is momentarily 'swept' forward in the direction of the median eminence to influence hypothalamic functions directly.