When the columns of the fornix reach the anterior commissural each column separates into a Precommissural and Postcommissural division. A minority of the fibers (precommissural fornix) go over the anterior commissure and proceed downward to synapse in the septal nuclei and nucleus accumbens. The postcommissural fornix, which is the large majority of fibers, arc downward and backward (behind the anterior commissure) to enter into the hypothalamus and synapse in the mammillary bodies. Thus the postcommissural fornix is a part of the classic Papez circuit (of the limbic system).
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