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Third (III) ventricle
Last reviewed: 20.11.2021
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The third (III) ventriculus (ventriculus tertius) occupies a central position in the diencephalon. The cavity of the ventricle looks like a sagittally located narrow slit, bounded by 6 walls: two lateral, upper, lower, anterior and posterior. The lateral walls of the third ventricle are the medial surfaces of the thalamuses facing each other, as well as the medial subthalamic regions below the hypothalamic furrow.
The lower wall, or bottom of the third ventricle, is the hypothalamus, its posterior (dorsal) surface facing the ventricle. In the lower wall, two protrusions (indentations) of the cavity of the third ventricle are distinguished: the deepening of the funnel (recessus infundibuli) and the visual recess (recessus opticus). The latter lies ahead of the visual crossover, between its front surface and the terminal (terminal) plate.
The anterior wall of the third ventricle is formed by a terminal plate, columns of the arch and anterior soldering. On each side, the column of the arch in front and the anterior section of the thalamus from behind restrict the interventricular opening (foramen interventriculare), through which the ventricle III cavity communicates with the lateral ventricle of this side.
The posterior wall of the third ventricle is the epithelamic adhesion, beneath which is an opening of the aqueduct of the brain. In the posterior regions of the third ventricle above the epithelial adhesion there is another protrusion of the cavity of the third ventricle - the supernumerary recessus (recessus suprapinealis). All the walls of the third ventricle from the inside, from the side of its cavity, are lined with ependyma. The upper wall is formed by a vascular base (tela choroidea). This base is represented by a soft (vascular) membrane, which, with two sheets (in the form of a duplication) under the roller of the corpus callosum and the vault penetrates into the cavity of the intermediate brain - into the third ventricle. The top sheet of the membrane fuses with the lower surface of the vault of the brain. At the level of the interventricular orifices, this leaf is turned and, heading back, passes into the lower sheet, which is actually the roof of the third ventricle. Further behind this leaf covers the pineal body on top and lies on the upper-posterior surface (roof) of the midbrain.
The upper and lower leaves of the soft shell of the brain, along with the underlying blood vessels, penetrate into the cavity of the lateral ventricle from the medial side through the vascular cleft. This gap is located between the upper (dorsal) surface of the thalamus and the lower surface of the arch.
Between the upper and lower leaves of the vascular base of the third ventricle, two internal cerebral veins (vv. Cerebri internae) are located in the connective tissue . These veins, when merged, form an unpaired large cerebral vein (v. Cerebri magna; galenic vein). From the side of the ventricle, the vascular base of the third ventricle is covered with an epithelial plate - the remnant of the posterior wall of the second cerebral bladder. The outcrops (villi) of the lower leaf of the vascular base together with the epithelial plate covering them hang down into the cavity of the third ventricle, where a vascular plexus (plexus choroideus) is formed. In the area of the interventricular orifice, this vascular plexus is connected to the vascular plexus of the lateral ventricle.