2. Introduction
• The cerebrum is the largest part of the human brain that fills most of the
cranial cavity.
• The cerebrum is a heavily, convoluted bilobed structure.
• The two lateral halves are called cerebral hemispheres.
• When the two cerebral, hemispheres are viewed together from above,
they assume the shape of an ovoid mass, which is broader behind than in
front.
• The widest transverse diameter corresponds with a line connecting the
two parietal tuberosities.
• A deep median cleft, the longitudinal cerebral fissure, incompletely
separates the two cerebral hemispheres.
• Both in front and behind, the cleft is complete, but in the central part the
cleft extends downwards up to the corpus callosum which is a large mass
of white fibres joining the two cerebral hemispheres across the median
plane.
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• The longitudinal cerebral fissure is occupied by the
following structures:
• 1. Falx cerebri (a sickle-shaped fold of dura mater).
• 2. Fold of arachnoid that follows the surfaces of the falx
cerebri.
• 3. Pia mater covering the medial surface of the falx cerebri.
• 4. Anterior cerebral arteries and veins (which lie in the
subarachnoid space between the arachnoid and the pia).
• Each cerebral hemisphere consists of:
• (a) an outer layer of grey matter called cerebral cortex,
• (b) an inner mass of white matter,
• (c) large masses of grey matter embedded in the basal part
of the white matter called basal ganglia/basal nuclei,
• (d) a cavity within it called lateral ventricle
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11. External Features of the Cerebral
Hemisphere
• The external features of the cerebral hemisphere include poles, surfaces, borders,
sulci, and gyri.
Poles
• Each cerebral hemisphere presents three poles – frontal, occipital, and temporal.
The anterior end of the hemisphere is the frontal pole and the posterior end
the occipital pole. The temporal pole is below and in front at the junction of orbital
and tentorial surfaces.
• • The frontal pole at the anterior end of the hemisphere is more rounded than the
occipital pole. It lies opposite the medial part of the superciliary arch.
• • The occipital pole at the posterior end of the hemisphere is more pointed than
the frontal pole. It lies at a short distance superolateral to the external occipital
protuberance.
• • The temporal pole between frontal and temporal poles points forwards. It fits
into the anterior part of the middle cranial fossa .
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13. Surfaces
• Each cerebral hemisphere has three surfaces – superolateral,
medial, and inferior.
• 1. The superolateral surface is most convex and most extensive. It
faces upwards and laterally and conforms to the corresponding half
of the cranial vault.
• 2. The medial surface is flat and vertical. It presents a thick C-
shaped cut surface of the corpus callosum.
• 3. The inferior surface is irregular to adopt the floors of anterior
and middle cranial fossae.
It is divided into two parts by a deep horizontal groove or sulcus,
the stem of lateral sulcus-
(a) a small anterior part, the orbital surface, and
(b) a large posterior part, the tento-rial surface.
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15. Borders
• Each cerebral hemisphere presents six borders .
• superomedial, superciliary, inferolateral, medial orbital, medial occipital and
inferomedial.
• 1. The superomedial border separates the superolateral surface from the medial
surface.
• 2. The superciliary border is at the junction of superolateral and orbital surfaces. It
lies just behind the superciliary arch hence its name strictly speaking, it is the
orbital part of the inferolateral border.
• 3. The inferolateral border -separates the superolateral surface from the tentorial
surface. Posteriorly this border exhibits a notch, the preoccipital notch about 3 cm
in front of the occipital pole. This notch is used as a useful surface landmark.
• 4. The medial orbital border - separates the medial surface from the orbital
surface.
• 5. The inferomedial/hippocampal border - surrounds the cerebral peduncle. It is
formed by the medial aspect of the uncus and parahippocampal gyrus.
• 6. The medial occipital border - separates the medial surface from the tentorial
surface.
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17. Sulci and Gyri
• The cerebral cortex (the surface layer of grey matter) is
highly extensive in man.
• To accommodate it in the limited space available
within the rigid cranial cavity, the surface of cerebral
hemisphere becomes folded, producing
numerous convolutions separated by fissures.
• These convolutions and fissures are
termed gyri and sulci respectively.
• In human brain the total surface area of cerebral
hemisphere is about 2000 cm but approximately two-
third of this is hidden from the surface view within the
walls of the sulci.
18. Main cerebral sulci
• Main cerebral sulci are fairly constant in
position and shape and include-
• Lateral sulcus (of Sylvius)
• Central sulcus (of Rolando)
• Calcarine sulcus
• Parieto-occipital sulcus
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20. Lobes of Cerebral Hemisphere
• The superolateral surface of the hemisphere is arbitrarily
divided into four lobes – frontal, parietal, temporal and
occipital with the help of:
• (a) three main sulci, central, lateral and parieto-occipital,
and (b) two imaginary lines.
• The first imaginary line is a vertical line joining the parieto-
occipital sulcus to the preoccipital notch.
• The second line is a backward continuation of the
horizontal part of the posterior ramus of the lateral sulcus
till it joins the first line
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22. Lobes of Cerebral Hemisphere
• The frontal lobe lies anterior to the central sulcus, and above the
posterior ramus of the lateral sulcus.
• The parietal lobe lies behind the central sulcus and in front of the
upper part of the first imaginary line. Below it is bounded by the
posterior ramus of lateral sulcus and the second imaginary line.
• The temporal lobe lies below the posterior ramus of lateral sulcus
and second imaginary line. It is separated from the occipital lobe by
the lower part of the first imaginary line.
• The occipital lobe lies behind the vertical line joining the parieto-
occipital sulcus and preoccipital notch.
23. Sulci and Gyri on the Superolateral Surface of the Cerebral
Hemisphere
24. Sulci and Gyri on the Medial Surface of the Cerebral
Hemisphere
25. Sulci and Gyri on the Inferior Surface of the Cerebral
Hemisphere
