Each cerebral hemisphere is composed of five lobes, called the frontal, parietal, occipital, temporosphenoidal, and central, or island of Reil.

The frontal lobe comprises the anterior portion of the brain, as far back as the fissure of Rolando or central sulcus, and as far toward the base as the fissure of Sylvius.

Fig. 40.   Lobes of the brain

Fig. 40. - Lobes of the brain.

The parietal lobe extends from the fissure of Rolando (central sulcus) in front to the parieto-occipital fissure behind. Below, it is limited anteriorly by the fissure of Sylvius, while its posterior portion merges into the temporosphenoidal lobe.

The occipital lobe extends posteriorly from a line joining the occipitoparietal fissure above to the pre-occipital notch below.

The temporosphenoidal lobe consists of that portion of the brain below the fissure of Sylvius, as far back as the pre-occipital notch. It occupies the middle fossa of the skull.

The central lobe or island of Reil, also called the insula, consists of five to seven convolutions which radiate upward; it can be seen by separating the two sides of the anterior portion of the fissure of Sylvius.

The Fissures And Convolutions Of The Brain

The surface of the brain is wrinkled or thrown into folds, producing elevations and depressions. The elevations are called convolutions or gyri, and the depressions, fissures or sulci.

The fissures are called main or subsidiary fissures, according to their importance. The five main fissures are the longitudinal fissure, which separates the hemispheres; the transverse fissure, which separates the cerebrum and cerebellum and communicates with the third ventricle; the fissure of Sylvius; the fissure of Rolando, or central fissure, and the parieto-occipital fissure.