Scanning electron microscopic studies on the embryonic development of the surface structures of the paraventricular organ in the Brown Leghorn chicken.

The development of the surface specialization of the paraventricular organ (PVO) was studied in the domestic chicken from the 10th embryonic day to the day of hatching by scanning electron microscopy. On the 10th embryonic day, the ventricular surface of the PVO was found to be covered with many oval-shaped processes. On the 12th embryonic day, an additional kind of elongated processes appeared in the dorsal area of the ventricular surface of the organ. From the 16th to 18th embryonic day, such elongated processes were present on the entire ventricular surface of the PVO. At the same stage, the elongated processes in the dorsal portion of the PVO began to form small, meshed networks over the surface of the ependyma. Both the oval-shaped processes and the elongated processes are thought to be dendritic terminals of the PVO neurons.