The cerebrum is the largest part of the brain. It is divided into two cerebral hemispheres. The outer area of each hemisphere — the cerebral cortex — has ridges called the gyri and shallow grooves called the sulci. A few large and distinct sulci divide the cerebrum into five different lobes — frontal, parietal, temporal, occipital, and insula. The central sulcus separates the frontal and parietal lobes. It also separates two functionally important gyri — the precentral and postcentral gyrus. The lateral sulcus separates the temporal lobe from the frontal and parietal lobes, while the parieto-occipital sulcus separates the parietal and occipital lobes. The smallest lobe—the insula, is present deep in the lateral sulcus. A deeper sulcus, known as the transverse cerebral fissure, marks the end of the occipital lobe and separates the cerebrum from the cerebellum. The cerebrum fits perfectly in the cranial cavity and is protected by it. The frontal lobes fit in the anterior cranial fossa, the temporal and parietal lobes lie in the middle cranial fossa, and the occipital lobes are present superior to the posterior cranial fossa.