The subcommissural organ.

TLDR: The anatomical situation in some vertebrate species is such as to suggest not only a secretion into the cerebrospinal fluid but also the possibility of direct release of substances into the vascular system.

Abstract: The subcommissural organ (SCO) consists of a secretory ependymal band and secretory hypendymal cells which are derived from the ependymal layer. Because of its intensive secretory activity and its cytochemical properties this general complex of cells assumes, among the ordinary ependymal and glial cells, a position similar to that of the neurosecretory cells among ordinary nerve cells. The secretory materials of the SCO are formed in distended cisternae of the rough endoplasmic reticulum. Using as examples the SCO’s of the tree frog (Hyla arborea), the dog, and the human embryo, the anatomical polarity of the SCO, i. e. the orientation to the ventricle as well as to the vascular bed, is discussed. The anatomical situation in some vertebrate species (e. g. the dog) is such as to suggest not only a secretion into the cerebrospinal fluid but also the possibility of direct release of substances into the vascular system. The function of the SCO is not understood with certainty.