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The hemispheres of the large brain
Medical expert of the article
Last reviewed: 04.07.2025
The telencephalon consists of two hemispheres of the cerebrum, separated by a longitudinal fissure and connected to each other in the depth of this fissure by means of the corpus callosum, the anterior and posterior commissures, and the commissures of the fornix. The cavity of the telencephalon consists of the right and left lateral ventricles, each of which is located in the corresponding hemisphere. The cerebral hemisphere consists of the outer covers - the cerebral cortex (mantle), the white matter lying deeper and the accumulations of gray matter located in it - the basal nuclei. The border between the telencephalon and the diencephalon following it passes through the place where the internal capsule adjoins the lateral side of the thalamus.
[ Hemisphere of the cerebrum
The cerebral hemisphere (hemispherium cerebralis) is covered on the outside by a thin plate of gray matter - the cerebral cortex. Each hemisphere has three surfaces: the most convex superolateral (facies superolateral, hemispherii), a flat medial surface facing the neighboring hemisphere (facies medialis hemispherii) and a lower surface (facies inferior hiispherii). The latter has a complex relief corresponding to the internal base of the skull. The surfaces of the cerebral hemispheres are separated from each other by edges: superior (margo superior), inferior lateral (margo inferior) and inferior medial (margo medialis). The most protruding areas of the hemisphere in front and behind are called poles: the frontal pole (polus frontalis), the occipital pole (polus occipitalis) and the temporal pole (polus tiporalis). The relief of the surfaces of the hemispheres is very complex due to the presence of more or less deep grooves of the cerebrum and the ridge-like elevations located between them - convolutions. The depth, length of the grooves and convex convolutions, their shape and direction are very variable.
Superolateral surface of the hemisphere
In the anterior part of each hemisphere of the brain is the frontal lobe (lobus frontalis). It ends in front with the frontal pole and is limited below by the lateral groove (sulcus lateralis; Sylvian groove), and behind by the deep central groove. The central groove (sulcus centralis; Rolandic groove) is located in the frontal plane. It begins in the upper part of the medial surface of the cerebral hemisphere, cuts across its upper edge, descends without interruption along the upper lateral surface of the hemisphere downwards and ends slightly before reaching the lateral groove.
Behind the central sulcus is the parietal lobe (lobus parietalis). The posterior border of this lobe is the parieto-occipital sulcus (sulcus parietooccipitalis). This sulcus is located on the medial surface of the cerebral hemisphere, deeply dissects the upper edge of the hemisphere and passes to its upper lateral surface.
The occipital lobe (lobus occipitalis) is located behind the parieto-occipital groove and its conditional continuation on the upper lateral surface of the hemisphere. Compared to other lobes, it is small in size. The occipital lobe ends with the occipital pole (polus occipitalis). The grooves and convolutions on the upper lateral surface of the occipital lobe are very variable.
The temporal lobe (lobus temporalis) occupies the lower lateral parts of the hemisphere and is separated from the frontal and parietal lobes by a deep lateral sulcus. The edge of the temporal lobe, covering the insular lobe, is called the temporal operculum (operculum temporale). The anterior part of the temporal lobe forms the temporal pole (polus temporalis). On the lateral surface of the temporal lobe, two grooves are visible - the superior and inferior temporal (sulci temporales superior et inferior), almost parallel to the lateral sulcus. The convolutions of the temporal lobe are oriented along the grooves.
The insular lobe, or island (lobus insularis, s. insula) is located deep in the lateral sulcus. This lobe can be seen by moving apart or removing the areas of the frontal, parietal, and temporal lobes that cover the insula, which are called the operculum. The deep circular sulcus of the insula (sulcus circularis insulae) separates the insula from the surrounding parts of the brain. On the surface of the insula there are insular convolutions, long and short (gyri insulae, longus et breves). Between the long gyrus, located in the posterior part of the insula and oriented from top to bottom and forward, and the short convolutions occupying the upper-anterior part of the insula, is the central sulcus of the insula (sulcus centralis insulae). The lower-anterior part of the insula is devoid of sulci and has a slight thickening - the insular threshold (limen insulae).
Medial surface of the hemisphere
All lobes of the hemisphere, with the exception of the insular, participate in the formation of its medial surface. Above the corpus callosum, separating it from the other parts of the hemisphere, is the sulcus of the corpus callosum (sulcus corporis callosi). Bends around the splenium of the corpus callosum from behind, this sulcus goes downwards and forwards and continues into the sulcus of the hippocampus, or hippocampal sulcus (sulcus hippocampi, s. hippocampalis). Above the sulcus of the corpus callosum is the cingulate sulcus (sulcus cinguli). This sulcus begins in front and downwards from the beak of the corpus callosum, rises upwards, then turns backwards and runs parallel to the sulcus of the corpus callosum. The sulcus ends above and behind the splenium of the corpus callosum as the subparietal sulcus (sulcus subparietalis). At the level of the splenium of the corpus callosum, the marginal part (pars marginalis, BNA) branches off upward from the cingulate sulcus, extending upward and backward to the upper edge of the cerebral hemisphere. Between the splenium of the corpus callosum and the cingulate sulcus is the cingulate gyrus (gyrus cinguli), which embraces the corpus callosum from the front, top, and back. Behind and below the splenium of the corpus callosum, the cingulate gyrus narrows, forming the isthmus of the cingulate gyrus (isthmus gyri cinguli). Further downward and anteriorly, the isthmus passes into a wider gyrus of the hippocampus, or parahippocampal gyrus (gyrus parahippocampalis), limited above by the splenium of the hippocampus. The cingulate gyrus, isthmus, and parahippocampal gyrus are known as the fornicate gyrus (gyrus fornicatus - BNA). In the depths of the hippocampal groove there is a rather thin grey strip, divided by small transverse grooves - the dentate gyrus (gyrus dentatus). The area of the medial surface of the hemisphere, located between the cingulate groove and the upper edge of the hemisphere, belongs to the frontal and parietal lobes.
In front of the upper edge of the central sulcus is the medial surface of the superior frontal gyrus, and directly adjacent to the indicated section of the central sulcus is the paracentral lobule (lobulus paracentralis), limited at the back by the marginal part of the cingulate sulcus. Between the marginal part in front and the parieto-occipital sulcus at the back is the precuneus - a section of the cerebral hemisphere belonging to the parietal lobe.
On the medial surface of the occipital lobe there are two deep grooves merging with each other at an acute angle, open to the back: the parieto-occipital groove, separating the parietal lobe from the occipital lobe, and the calcarine groove (sulcus calcaneus). The latter begins on the medial surface of the occipital pole and runs forward to the isthmus of the cingulate gyrus. The area of the occipital lobe lying between the parieto-occipital and calcarine grooves and having the shape of a triangle, with its apex facing the place of confluence of these grooves, is called the wedge (cuneus). The calcarine groove, clearly visible on the medial surface of the hemisphere, limits the lingual gyrus (gyrus hingualis) from above, extending from the occipital pole behind to the lower part of the isthmus of the cingulate gyrus; below the lingual gyrus is the collateral groove (sulcus collateralis), belonging to the lower surface of the hemisphere.
The lower surface of the hemisphere
The relief of the lower surface of the hemisphere is very complex. The anterior sections of this surface are formed by the frontal lobe of the hemisphere, behind which the temporal pole protrudes, and also the lower surfaces of the temporal and occipital lobes are located, passing into each other without noticeable boundaries.
On the lower surface of the frontal lobe, somewhat lateral to and parallel to the longitudinal fissure of the cerebrum, runs the olfactory groove (sulcus olfactorius). Adjacent to it below are the olfactory bulb and the olfactory tract, which passes behind into the olfactory triangle. In the area of this triangle, the medial and lateral olfactory stripes (striae olfactoriae medialis et lateralis) are visible. The area of the frontal lobe between the longitudinal fissure of the cerebrum and the olfactory groove is called the straight gyrus (gyrus rectus). The surface of the frontal lobe, lying lateral to the olfactory groove, is divided by shallow orbital grooves (sulci orbitales) into several orbital convolutions (gyri orbitales), which vary in shape, location and size.
In the posterior part of the inferior surface of the hemisphere, the collateral sulcus is clearly visible, located inferiorly and lateral to the lingual gyrus on the inferior surface of the occipital and temporal lobes, lateral to the parahippocampal gyrus. Slightly anterior to the anterior end of the collateral sulcus is the rhinal sulcus (sulcus rhinalis). It borders the curved end of the parahippocampal gyrus, the hook (lincus), on the lateral side. Lateral to the collateral sulcus is the medial occipitotemporal gyrus (gyrus occipitotemporalis medialis). Between this gyrus and the lateral occipitotemporal gyrus (gyrus occipitotemporalis lateralis), located outside of it, is the occipitotemporal sulcus (sulcus occipitotemporalis). The boundary between the lateral occipitotemporal and inferior temporal gyri is not a groove, but the inferolateral edge of the cerebral hemisphere.
A number of brain regions located mainly on the medial surface of the hemisphere and serving as a substrate for the formation of such general states as wakefulness, sleep, emotions, behavioral motivations, etc., are distinguished under the name of the limbic system. These reactions were formed in connection with the primary functions of smell (in phylogenesis), therefore their morphological basis are the brain regions that develop from the lower lateral regions of the cerebral vesicle and belong to the so-called olfactory brain (rhinencephalon). The limbic system consists of the olfactory bulb, olfactory tract, olfactory triangle, anterior perforated substance located on the lower surface of the frontal lobe (peripheral region of the olfactory brain), as well as the cingulate and parahippocampal (together with the hook) gyri, dentate gyrus, hippocampus (central region of the olfactory brain) and some other structures. The inclusion of these parts of the brain in the limbic system was possible due to the common features of their structure (and origin), the presence of mutual connections and the similarity of functional reactions.
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