Observations on the pineal system in the hamster. II. Fine structure of the deep pineal

The fine structure of the deep pineal, a mass of pineal parenchyma positioned in the roof of and caudal to the pineal recess is described. The fine structure of deep pineal is similar to earlier descriptions of superficial pineal. The parenchymal cell displays abundant mitochondria, many of which contain a tubular internal structure, a prominent Golgi apparatus, and smooth and granular endoplasmic reticulum. The parenchymal cells are extensively branched and terminate in club‐like endings. Pineal cell process terminations contain a profusion of vesicles of varying size, many of which contain an electron‐dense granule. The granules are presumed to be associated with the secretory product of the parenchymal cell. The deep, unlike the superficial, pineal contains a relatively high concentration of glial cells and processes, some of which contain mitochondria with a unique internal structure.