The corpus callosum is a broad, flat band of nerve fibres deep in the middle of the brain, at the bottom of the longitudinal fissure between the two hemispheres. It joins the left and right hemispheres and roofs the lateral ventricles. [1]
The 3D brain needs JavaScript. The text below still says where the corpus callosum is and what it does.
Slice
Opens cut by a side (sagittal) slice through the corpus callosum. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Where it is
It forms the floor of the longitudinal fissure that separates the two cerebral hemispheres, and part of it forms the roof of the lateral ventricles. [1]
Deep within the cerebrum, beneath the cerebral cortex: a single midline structure, not a pair. [1][2]
The cingulate gyrus lies immediately above it, separated from it by the callosal sulcus. [3][1]
Front to back it has four parts: the thin rostrum (“beak”) underneath, the genu (“knee”) curving at the front, the trunk or body, and the splenium, the thickest part at the back, which lies over the midbrain. [1]
What it does
The major pathway for communication between the two hemispheres of the cerebral cortex. [2]
Thin axons in the genu join the left and right prefrontal cortex; thicker axons in the trunk join the motor areas; the splenium carries somatosensory information between the parietal lobes and visual information between the occipital lobes. [1]
Fibre type matches the job: thinner, lightly myelinated fibres conduct more slowly and join association and prefrontal areas, while thicker, fast-conducting fibres join the visual and motor areas. [1]
It is found only in placental mammals; marsupials, monotremes, birds, reptiles, amphibians and fish do not have one, and in marsupials the anterior commissure does this job instead. [1]
Connections
Its fibres fan out into the white matter of each hemisphere: those curving forward from the genu into the frontal lobes form the forceps minor, those curving back from the splenium into the occipital lobes form the forceps major. [1]
Between the two, the tapetum (“carpet”) runs sideways into the temporal lobes; together with the anterior commissure it joins the left and right temporal lobes. [1]
Blood supply: the anterior cerebral arteries arch over the genu and run along the trunk, supplying the front four-fifths of it. [1]
Inside it
It is white matter: a flat bundle of commissural fibres, 200 to 300 million axons, divided into separate tracts (rostrum, genu, trunk, splenium) that join different parts of the hemispheres. [1]
Its fibres are believed to keep gaining myelin into a person’s thirties, with peak growth in the first decade of life. [1]
Other names
Latin for “tough body”. Also called the callosal commissure. [1]
Size
The largest white-matter structure in the human brain: about 10 cm long, with 200 to 300 million axons. [1]
A meta-analysis of 49 studies since 1980 found no sex difference in its size, whether or not brain size was accounted for. [1]
On this model the corpus callosum measures about 92 mm front to back, 39 mm top to bottom and 51 mm side to side (the box it fits in, not its volume). [4]
Centre of the corpus callosum compared with the centre of the left lateral ventricle: 6 mm further forward, 10 mm higher, 17 mm closer to the midline; 20 mm apart in a straight line. [4]
Centre of the corpus callosum compared with the centre of the left cingulate gyrus: 5 mm further forward, 4 mm lower, 9 mm closer to the midline; 11 mm apart in a straight line. [4]
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.