The mammillary bodies are a pair of small round bumps on the underside of the brain, side by side at the back of the hypothalamus, at the ends of the arches of the fornix. They relay memory signals from the hippocampus on to the thalamus. [1]
The 3D brain needs JavaScript. The text below still says where the mammillary bodies are and what they do.
Slice
Opens cut by a side (sagittal) slice through the mammillary bodies. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
On the undersurface of the brain, one each side of the midline, at the ends of the anterior arches (columns) of the fornix. [1]
They are part of the diencephalon, and neuroanatomists often count them as part of the back (posterior) part of the hypothalamus. [1]
Front to back the hypothalamus has four regions, preoptic, supraoptic, tuberal and mammillary; the mammillary bodies sit in the last. [2]
What it does
They act as a relay for signals coming from the hippocampi and amygdalae, passing them to the thalamus through the mammillothalamic tract. [1]
With their projections to the anterior thalamus they are important for recollective memory; in studies in rats, damage to the medial mammillary nucleus impaired spatial memory. [1]
They are the third link of the Papez circuit, between the fornix and the anterior thalamic nuclei. [3]
Honest limit: their exact function is still not clear. [1]
Connections
In: the fornix, whose columns descend through the wall of the third ventricle and end in them. [4]
Out: the mammillothalamic tract (bundle of Vicq d’Azyr), heavily myelinated fibres to the anterior nuclei of the thalamus; finer branches descend as the mammillotegmental fasciculus to the tegmental nuclei of the midbrain. [5]
The lateral mammillary nucleus has two-way connections with the dorsal tegmental nucleus; the medial one connects with the ventral tegmental nucleus. [1]
Inside it
Two groups of nuclei in each body: the medial mammillary nuclei and the lateral mammillary nuclei. [1]
Other names
Mammillary body (one of the pair); also spelled mamillary bodies; Latin corpora mammillaria. [1]
Size
On this model the left mammillary body measures about 5 mm front to back, 5 mm top to bottom and 4 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [6]
Centre of the left mammillary body compared with the centre of the hypothalamus: 6 mm further back; 6 mm apart in a straight line. [6]
Centre of the left mammillary body compared with the centre of the left fornix: 13 mm further forward, 12 mm lower, 10 mm closer to the midline; 20 mm apart in a straight line. [6]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.