The mammillary region or mammillary body is the final group of nuclei in the medial zone. Four nuclei comprise this region: medial, intermediate, lateral mammillary, and posterior hypothalamic. The best defined is the medial mammillary nucleus, as it is the primary site for the termination of axons from the postcommissural fornix. This pathway originates from the subiculum of the hippocampal complex and plays a key role in memory. The medial mammillary nuclei also connects to structures of the limbic system.