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|Brain: Third ventricle|
Scheme showing relations of the ventricles to the surface of the brain.
|Latin||ventriculus tertius cerebri|
The third ventricle (ventriculus tertius) is one of four connected fluid-filled cavities comprising the ventricular system within the human brain. It is a median cleft in the diencephalon between the two thalami, and is filled with cerebrospinal fluid (CSF).
It is in the midline, between the left and right lateral ventricles. Running through the third ventricle is the Interthalamic adhesion, which contains thalamic neurons and fibers that may connect the two thalami.
The third ventricle communicates with the lateral ventricles anteriorly by the interventricular foramina (of Monro). It also communicates with the fourth ventricle posteriorly by the cerebral aqueduct (of Sylvius).
The third ventricle, like other parts of the ventricular system of the brain, develops from the central canal of the neural tube. Specifically, it originates from the portion of the tube that is present in the developing prosencephalon, and subsequently in the developing diencephalon.
The third ventricle is bounded by the thalamus and hypothalamus on both the left and right sides. The lamina terminalis forms the anterior wall. The floor is formed by hypothalamic structures, and can be opened between the mamillary bodies and the pituitary gland; this is called an endoscopic third ventriculostomy. The roof is formed by the ependyma, lining the undersurface of the tela choroidea of the third ventricle.
There are two protrusions on the anterior aspect of the third ventricle:
- the supra-optic recess (above the optic chiasma)
- the infundibular recess (above the pituitary stalk).
Additionally, there are two protrusions on the posterior aspect, above the cerebral aqueduct:
- the suprapineal recess (above the pineal gland)
- the pineal recess (protruding into the stalk of the pineal gland)
In casts of the ventricular system, a small hole may be seen in the body of the third ventricle. This is formed where the two thalami are joined together at the interthalamic adhesion (not seen in all people).
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