thalamic nucleus median nucleus of thalamus BTO:0002454 BrendaTissueOBO Small groups of nonspecific nerve cells scattered in the periventricular gray substance, separating the medial part of the thalamus from the ependyma of the third ventricle, and partly forming the interthalamic adhesion; included in the group are the anterior and posterior paraventricular nuclei, nucleus parataenialis, nucleus commissuralis rhomboidalis, and nucleus reuniens. median nuclei of thalamus nucleus mediani thalami