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Structure
The cerebrum comprises the largest part of the brain. It lies in front or on top of the brainstem and, in humans, is the largest and best-developed of the five major divisions of the brain. The cerebrum is the newest structure in the phylogenetic sense, with mammals having the largest and most developed structures among all species.

The cerebrum is composed of the following regions:
 * Cerebral cortex: Layer of grey matter (type of nervous tissue involved in information processing) on the surface of the cerebrum.
 * White Matter: Type of nervous tissue involved in relaying signals between grey matter areas.

Cerebral Cortex
The cerebral cortex, or the lining of gray matter on the cerebrum, is found only in mammals. In larger mammals, including humans, the surface of the cerebral cortex folds to create gyri (ridges) and sulci (furrows). These structural adaptations increases surface area without adding volume, increasing surface-area-to-volume ratio.

Cerebral Hemispheres
The cerebrum can be split into two cerebral hemispheres, the right and the left side. The right side of the cerebral hemisphere controls and processes signals from the left side of the body, while the left hemisphere is concerned with the right side of the body. (See: Lateralization of Brain Function for more about the differences between the two cerebral hemispheres.)

Development
In the developing vertebrate embryo, the neural tube subdivides into four unseparated sections which then develop further into distinct regions of the CNS; these are the prosencephalon, the mesencephalon the rhombencephalon and the spinal cord. The prosencephalon develops further into the telencephalon (forebrain or cerebrum), and the much smaller diencephalon which develops into the optic vessels and the hypothalamus. The telencephalon then forms two lateral telencephalic vesicles which develop into the left and right cerebral hemispheres.