Overview

Axons≈200 million

Length (sagittal)≈10 cm

In midsagittal section the corpus callosum is a C-shaped white band ≈10 cm long. From front to back it has:
• a thin rostrum, continuous with the lamina terminalis;
• a curved genu;
• a long body (trunk);
• a narrow isthmus;
• a thick posterior splenium.
It forms the roof of most of the lateral ventricles. Below it the septum pellucidum stretches down to the fornix, and above it lie the cingulate gyrus and the pericallosal arteries, which are branches of the ACA.

Its fibres are largely homotopic, connecting mirror-image cortical areas, and they are topographically arranged:
• the genu links the prefrontal cortices, curving forward as the forceps minor;
• the body links the premotor, motor, somatosensory and parietal cortices;
• the splenium links the occipital and posterior temporal lobes (visual information), sweeping back as the forceps major.
Other commissures are the anterior commissure (olfactory and anterior temporal), the posterior commissure (pupillary light reflex) and the hippocampal commissure. The corpus callosum lets each hemisphere share information gathered by the other, e.g. naming an object felt with the left hand requires transfer to the left-hemisphere language areas.

Location: Floor of the longitudinal cerebral fissure, roofing the lateral ventricles; above the septum pellucidum, fornix and thalami.

Parts & subdivisions

Rostrum
Thin anterior-inferior part continuous with the lamina terminalis.
Genu
Anterior bend; prefrontal fibres (forceps minor).
Body (trunk)
Fibres of the frontal and parietal motor and sensory areas.
Isthmus
Narrowing in front of the splenium; posterior parietal and superior temporal fibres.
Splenium
Thick posterior end; occipital (visual) fibres (forceps major); supplied by the PCA.

Anatomy

Arterial supply: Pericallosal branches of the anterior cerebral artery (rostrum, genu, body); splenial branches of the posterior cerebral artery (splenium).
Development: Forms between ≈12 and 20 weeks from the lamina terminalis, growing from front to back (except the rostrum, which forms last). Agenesis, complete or partial, may be isolated and asymptomatic or part of syndromes (e.g. Aicardi). Imaging shows parallel lateral ventricles with "colpocephaly".

Function

Interhemispheric transfer of sensory, motor and cognitive information
Coordination of bimanual movements
Integration of the two visual hemifields
Shares language and attentional processing between the hemispheres

Clinical significance

Disconnection (split-brain) syndrome

After corpus callosotomy (for drop attacks in refractory epilepsy) or a callosal infarct, information confined to the right hemisphere cannot reach the left-hemisphere language areas. The patient cannot name objects held in the left hand or flashed in the left visual field, and may show alien-hand phenomena. Splenial plus left occipital damage causes alexia without agraphia.

Callosal lesions on MRI

• Multiple sclerosis: callososeptal-interface plaques and "Dawson fingers".
• Glioblastoma or lymphoma crossing the corpus callosum: "butterfly glioma".
• Diffuse axonal injury: lesions in the splenium.
• Marchiafava–Bignami disease in chronic alcohol use.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.