a triangular group of large magnocellular neurons in the periventricular zone of the anterior half of the hypothalamus. The cells of the nucleus are similar to those of the supraoptic nucleus; the axons of about 20% of their number join in the formation of the supraopticohypophysial tract and are functionally associated with the posterior lobe of the hypophysis; they project fibers to the brainstem nuclei (dorsal motor nucleus and solitary nucleus) and to the intermediolateral cell column of the spinal cord at thoracic, lumbar, and spinal levels; similar descending autonomic fibers arise from the lateral and posterior hypothalamic nuclei. SYN: filiform nucleus, nucleus filiformis, nucleus paraventricularis hypothalami.