Forebrain: Olfactory Lobes and Cerebrum

A. The Human brain : The human brain -- studied as a whole under the name encephalology -- divides into three main parts: forebrain, midbrain and hindbrain. The forebrain itself begins with the olfactory lobes, which are highly reduced in humans and covered by the cerebrum on every side except the ventral surface; each lobe has an olfactory peduncle and an olfactory bulb.

ii. Cerebrum : The cerebrum is the brain's largest part, making up about 85% of its total mass. A deep median longitudinal fissure splits it into right and left cerebral hemispheres, which stay internally connected by a thick band of nerve fibres, the corpus callosum (the largest commissure of the mammalian brain, with an anterior fold, the genu, and a posterior fold, the splenium). The cerebrum's outer surface, the cerebral cortex, is grey matter; its deep interior, the cerebral medulla, is white matter. The surface is thrown into many folds -- convolutions (gyri) and grooves (sulci) -- that massively increase the surface area available to pack in neurons. Three deep sulci divide each hemisphere into four main lobes: the central sulcus separates the frontal from the parietal lobe, the parieto-occipital sulcus separates the parietal from the occipital lobe, and the lateral (Sylvian) sulcus separates the temporal lobe from the frontal and parietal lobes; because these sulci are incomplete, the lobes are not sharply demarcated, and a fifth, median lobe -- the insula -- lies folded deep within the lateral sulcus.

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