The mammillary bodies (mamillary bodies) are a pair of small round bodies, located on the undersurface of the brain, that, as part of the diencephalon form part of the limbic system. They are located at the ends of the anterior arches of the fornix. They consist of two groups of nuclei, the medial mammillary nuclei and the lateral mammillary nuclei. Both are linked to the hypothalamus via a nerve path called the fornix and feature a series of neural projections that connect to other parts of the brain. The lateral mammillary nucleus contains the largest neurons in the system while the medial nuclei of the mammillary bodies are comprised of one to five subnuclei depending on the type of animal. Neuroanatomists have often categorized the mammillary bodies as part of the hypothalamus. Connections They are connected to other parts of the brain and act as a relay for impulses coming from the amygdalae and hippocampi, via the mamillo-thalamic tract to the thalamus. This circuit, from amygdalae to mammillary bodies, and then on to the thalamus, is part of the larger Papez circuit. Function Mammillary bodies, and their projections to the anterior thalamus via the mammillothalamic tract, are important for recollective memory. The medial mammillary nucleus is mainly responsible for the spatial memory deficits that are seen in rats with mammillary body lesions. They are believed to add the element of smell to memories.