Cerebrum is the largest part of the human brain, making up approximately 85 percent of the brain’s weight; its large surface area (cortex) and intricate development account for the superior intelligence of humans, compared with other animals.

The cerebrum is divided by a longitudinal fissure (indentation) into right and left, miror-image hemispheres. The corpus callosum is the slab of white nerve fibers that connects these two cerebral hemispheres and transfers important information from one to the other.

Two well-defined, fluid filled spaces call ventricles are found within each of the two hemisphere, by means of small openings called the foramen of Monro. The third ventricle leads into a fourth ventricle, locate in front of the medulla called the aqueduct of Sylvius. Cerebrospinal fluid (CSF), which circulates within these cerebral ventricles and around the spinal cord, serves to protect the internal portion of the brain from varying pressures and to transport chemical substances within the nervous system.
CSF is formed largely in the lateral ventricles from the choroid plexus, a closely knit bed of tiny blood vessels.

Each cerebral hemisphere consists of an outer layer of gray matter called the cerebral cortex. The cortex is composed of layers of unmyelinated cells, which in turn cover an inner mass of myelinated fibers called white matter. Myelinated fibers connect the cerebrum with other parts of the brain (protection fibers); the front of the brain to the back portion; different areas on the same side of the cerebrum (association fibers); and on side of the brain to the other side.

Each cerebral hemisphere is divided by fissures into five lobes. Four of the lobes are named after the overlying bones of the cranium: