(telencephalon) n. the largest and most highly developed part of the brain, composed of the two cerebral hemispheres, separated from each other by the longitudinal fissure in the midline (see illustration). Each hemisphere has an outer layer of grey matter, the *cerebral cortex, below which lies white matter containing the *basal ganglia. Connecting the two hemispheres at the bottom of the longitudinal fissure is the corpus callosum, a massive bundle of nerve fibres. Within each hemisphere is a crescent-shaped fluid-filled cavity (lateral *ventricle), connected to the central third ventricle in the *diencephalon. The cerebrum is responsible for the initiation and coordination of all voluntary activity in the body and for governing the functioning of lower parts of the nervous system. The cortex is the seat of all intelligent behaviour. —cerebral adj.... cerebrum
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