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1. Cerebrum - Internal
Structures
Prof. Saleh M. Al-Dhaheri
Head of Human Anatomy & Histology Department
Sana’a University

2. Introduction
• An outer layer of grey matter (cerebral cortex) of the
surface.
• White matter forming the core of the hemispheres.
• Basal ganglia is a collection of the grey matter embedded in
the white matter core.
• Lateral ventricles is a cavity of the cerebral hemispheres.
• The White Matter of The Cerebral Hemispheres consists of
myelinated nerve fibres which are devoid of neurolemmal
sheaths.
• There are 3 types of fibres:
1. Association fibres.
2. Commissural fibres.
3. Projection fibres.

3. Association Fibres
• Connect the different cortical areas in the same hemisphere.
• They interrelate the functions of the different areas of the
cortex & integrate the activates of cortex as a whole.
• They are 2 types:
– Short Association Fibres: they consist of U-shaped bands
called arcuate fibres lying just deep to the cerebral cortex.
They connect adjacent gyri with one another.
– Long Association Fibres :They include 4 bundles of long
fibres which connect the different lobes of the hemisphere
together. These 4 bundles include:
1. The superior longitudinal bundle: it is a largest associated
bundle. It begins in the anterior part of the frontal lobe. It passes
backward above the insula then divided into:
– Superior band enters the occipital lobe.
– Inferior band turns downwards to enter the temporal lobe.
It connect the frontal, occipital & temporal cortical areas together.

4. Association Fibres
2. The uncinate bundle: it is U-shaped band which is sharply bent
over itself. It begins at the orbital gyri of the frontal lobe. It arches
over the stem of the lateral sulcus to end in the anterior part of
the temporal lobe. It connect the gyri of the orbital surface of the
frontal lobe & Brocha’s speech area with the cortex of the
anterior part of the temporal lobe.
3. The cingulum: it is a long curved bundle lying in the medial
aspect of the cerebral hemisphere forming an incomplete circle
around the corpus callosum. It begins below the rostrum of the
corpus callosum in the region of the anterior perforated
substance. It extends backwards in the cigulate gyrus then
curves downwards in the isthmus then passes forwards in the
hippocampal gyrus to end in the uncus. Throughout its course it
gives off fibres to & receive additions from the different cortical
areas on the medial surface associating them.
4. The inferior longitudinal bundle: it is a bundle association fibres
running horizontally close to the tentorial surface of the cerebral
hemisphere. It begins near the occipital pole. It connect the
cortical areas of the tentorial surface together.

5. Association Fibres

6. Commissural Fibres
• Is a band of white matter connecting a part of the
CNS on one side with the same part on the
opposite side.
• They co-ordinate of the activates of the Rt. & Lt.
cerebral hemisphere. They are collected in the
following bundles:
1. The corpus callosum
– It is the largest & the main commissure of the brain. Its
fibres connect nearly all the symmetrical areas of the 2
hemispheres (except olfactory bulbs and temporal poles ).
– Site: It lies at the bottom of the median longitudinal
fissure. Its inferior surface is attached to the fornix by the
septum pellucidum.
– Parts of the corpus callosum:

7. Corpus Callosum
– Rostrum: it is the downward tapering part of the copus callosum. It is
connected to the optic chiasma by a thin sheet of grey matter. It forms
the floor of the anterior horn of the lateral ventricles. The fibres of the
rostrum connect the orbital surfaces of the 2 frontal lobes.
– Genu: it is the most anterior part of the corpus callosum. Its posterior
surface is connected to the septum pellucidum in the median plane &
on each side it forms the anterior wall of the anterior horn of the lateral
ventricles. The fibres passing through the genu curve forwards &
medially on each side to form an arch called the forceps minor which
connects the anterior parts of th 2 frontal lobes together.
– Body (trunk): it is the main part of the corpus callosum. Its lower
surface is attached in the median plane to the septum pellucidum
(anteriorly) & to the body of the fornix (posteriorly). On each side of the
median plane, the lower surface of the body of corpus callosum forms
the roof of the anterior horn & central part of each lateral ventricles.
The fibres of the body pass transversely, but after crossing the middle
line they diverge upwards, laterally & downwards in each hemisphere
to connect the different areas of the parietal lobe & post part of frontal
lobe of both sides together.

8. – Splenium: it is the rounded posterior end of the corpus callosum. It
overlies the pineal body & the dorsal aspect of midbrain & is separated
from the roof of the 3rd ventricle by a thin sheet of pia matter called tela
choroidae. Most of the fibres of the splenium curve backwards &
medially on each side through the occipital lobe forming the forceps
major. Some of its fibres with the posterior part of the body of corpus
callosum pass laterally & downwards forming the roof & lateral wall of
the posterior horn of the lateral ventricles. These fibres constitutes the
tapetum of corpus callosum.
Corpus Callosum

9. Corpus Callosum

10. 2. The anterior commissure
• It is a small runded bundle which crosses the median plane behind
the lamina terminalis and infront of the columns of the fornix
forming a part of the anterior wall of the 3rd ventricle.
• Its fibres connect the olfactory bulbs & the anterior part of the
temporal lobes.
3. The habenular commissure
• It is a bundle of commissural fibres which cross the median plane
above the root of the pineal body.
• It connects the habenular nuclei of the 2 sides of the epithalamus
together.
4. The posterior commissure
• It is a rounded bundle of commissural fibres that cross the median
plane behind the upper end of the aqueduct of midbrain.
• It connects the superior colliculus,the pretectal nucleus & the
medial longitudinal bundle of both sides of the midbrain together.
Commissural Fibres

11. The fornix & the hippocampal
commissure
• The fornix: is an arched structure formed by the axons
of the cells of the hibbocampus. These axons are
projection fibres which will finally end in the mammillary
body.
• Structure: Each fornix is formed of the following parts:
1. Crus (posterior column): posteriorly
• The axons of the hippocampal cells spread to form the alveus.
• Fibres of the alveus collect form a band of fibres medial to the
alveus called the fimbria.
• Fibres of the fimbria curve upwards to form the crus of the fornix
which turns rund the posterior end of the thalamus.
2. Body of the foenix:
• The Rt. & Lt. crura pass upwards & medially approaching other
beneath the splenium of copus callosum, then each crus
proceeds as the body of the fornix.
• The bodies of the 2 fornices are connected together by the
hippocampal commissure forming a common triangular body.
• The upper surface of the common body is attached to the
undersurface of the copus callosum by a membrane called

12. septum pellucidum. On each side of this septum, the body of
the fornix lies in the floor of the central part of the lateral
ventricles.
• The lower surface of the common body rests on the upper
surface of the 2 thalami & the ependymal roof of th 3rd ventricle.
3. Column (anterior column):
• Is the download continuation of each body which descends
infront of the interventricular f. & behind the anterior
commissure to end in the mammilary body of the
hypothalamus.
The fornix & the hippocampal
commissure

13. Projection Fibres
• Definition: they are afferent & efferent fibres of the
cerebral cortex which pass through the internal capsule &
connect the cerebral cortex with lower centre.
• NB: They are collected in the internal capsule.
• Types → the projection fibres are:
A. Ascending fibres (thalamic radiation): They are the fibres
which radiate from the thalamus & metathalamus to the
cerebral cortex:
• Anterior thalamic radiation: ascends from the anterior & medial
nuclei of the thalamus to the frontal lobe.
• Superior thalamic (sensory) radiation: ascends from the posterior
ventral nucleus of the thalamus to the postcentral gyrus.
• Posterior thalamic radiation which consists of:
– Optic radiation: the fibres which arise from the lateral geniculate
body & pass to the visual sensory area of the occipital lobe.
– Auditory radiation: the fibres which arise from the medial geniculate
body & pass to the auditory sensory area of the temporal lobe.

14. Projection Fibres
B. Descending fibres (mainly pyramidal & extrapyramidal)
→ they include:
• Cortico-spinal fibres: arise from motor area in the precentral
gyrus & descend to the anterior horn cells of the spinal cord.
• Cortico-bulbar fibres: arise from the precentral gyrus & descend
to the motor nuclei of the ctanial nerves in the brainstem.
• Cortico-pontine fibres → which constitute a part of the
pontocerebellar pathway & include:
– Fronto-pontine fibres.
– Parieto-pontine fibres.
– Occipito-pontine fibres.
– Temporo-pontine fibres.
• Cortico-rubral fibres: descending from the frontal lobe to the red
nucleus in the midbrain.
• Cortico-striate fibres: descending from the cerebral cortex to the
corpus striatum.

15. Projection Fibres

16. Thank You