INTRODUCTION:-
It is a median left between the two thalami. It
represents the cavity of the diencephalon. It is lined by ependyma.
COMMUNICATION:-
ANTEROSUPERIORLY:- On each side, it communicates
with the lateral ventricle through the interventricular foramen. This Foramen is
anteriorly bounded by a column of fornix and posteriorly by the tubercle of the thalamus.
POSTEROINFERIORLY:- It communicates with fourth
ventricle through the cerebral aqueduct.
RESSCES:-
These are extensions of the cavity.
- Supraspinal
- Pineal
- Infundibulum
- Optic.
BOUNDARIES:-
1. ANTERIOR WALL:-
It is bounded by
- Lamina terminals.
- Anterior commissure.
- The anterior column of the fornix.
2. POSTERIOR WALL:-
It is bounded by
- Pineal body.
- Posterior commissure.
- Cerebral aqueduct.
ROOF:-
- It is formed by the ependymal lining under the surface of the choroid of the third ventricle.
- The choroid plexus of third ventricle projects downwards from the roof.
- At the junction of the roof with the anterior and the lateral wall, there is the interventricular foramen.
FLOOR:-
It is formed by hypothalamic structure:-
- Optic chiasma.
- Tubercinerium .
- Infundibulum.
- Mammillary body.
- Posterior perforated substance.
- Tegmentum of the midbrain.