Stock Photo: BRAIN, SCAN. BRAIN, SCAN The brain is divided into two hemispheres bridged by a mass of nerve fibers, the corpus callosum. The brain as a whole (encephalon) is composed of these areas along with the brain stem (the prolongation of the spinal cord), and the cerebellum (a sort of branch circuit located in the posterior region of the skull). Deep grooves separate the brain into lobes designated by the names of the overlying skull bones: frontal, parietal, temporal, occipital. Seen here, a normal