The Mammilary Bodies are a pair of small round structures located on the underside of the brain at the end of the Fornix - which is connected to the Hippocampus. ( see diagram at Wikipedia )

They are believed to be associated with memory recall, as damage, which can occur as a result of physical injury, or due to Alzheimer's diseaseplugin-autotooltip__plain plugin-autotooltip_bigAlzheimer's disease

"Alzheimer’s disease is a chronic progressive neuro-degenerative disorder characterised by three primary groups of symptoms. The first group (cognitive dysfunction) includes memory loss, language difficulties, and executive dysfunction (that is, loss of higher level planning and intellectual coordination skills). The second group comprises psychiatric symptoms and behavioural disturbances — for example, depression, hallucinations, delusions, agitation — collectively termed … or Schizophreniaplugin-autotooltip__plain plugin-autotooltip_bigSchizophrenia

"Schizophrenia is a mental disorder characterized by abnormal social behavior and failure to understand what is real. Common symptoms include false beliefs, unclear or confused thinking, auditory and visual hallucinations, reduced social engagement and emotional expression, and a lack of motivation.", radically affects memory.

Their exact function is unknown.