The mammillary 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.
Neuroanatomists have often categorized the mammillary bodies as part of the hypothalamus.
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 thethalamus.
This circuit, from amygdalae to mammillary bodies, and then on to the thalamus, is part of the larger Papez circuit.
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.