Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovskyi 2008

Special Part
Nervous system, systema nervosum - Special Part
Brain - Embryogenesis of the brain - Fourth ventricle

The Fourth ventricle, ventriculus quartus, is the remnant of the cavity of the Hindbrain vesicle. In shape, it resembles a tent, with a distinguished floor and roof (Fig. 143 A, B).

The floor of the fourth ventricle is formed by the posterior surface of the Medulla Oblongata and the Pons. It resembles a rhombus, which is why it is called the Rhomboid fossa, fossa rhomboidea. The fourth ventricle communicates with the Third ventricle via the cerebral aqueduct, which opens into the superior angle of the rhomboid fossa, while its inferior angle is covered by the obex and opens into the central canal of the Spinal Cord. The lateral angles of the rhomboid fossa end blindly as lateral recesses, recessus lateralis.

The roof of the fourth ventricle, tegmen ventriculi quarti, is formed by two medullary vela: the superior, velum medullare superius, and the inferior, velum medullare inferius, as well as the choroid lamina of the fourth ventricle (lamina choroidea ventriculi quarti).

The superior medullary velum, velum medullare superius, is a thin, triangular lamina of White matter located between the superior cerebellar peduncles, forming the upper part of the roof of the fourth ventricle.

The inferior medullary velum, velum medullare inferius, is formed by a thin neural lamina, which is a remnant of the posterior wall of the primary Brain vesicle and extends to the peduncles of the flocculus. Together with the tela choroidea, they form the lower part of the roof of the fourth ventricle.

In the midline of the inferior medullary velum, there is an opening—the median aperture, apertura mediana (foramen of Magendie)—and located more laterally are two other openings—the lateral apertures, apertura lateralis (foramen of Luschka). Through these openings, the cavity of the fourth ventricle communicates with the subarachnoid space, spatium subarachnoideum, of the brain.

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Fig. 143 A. Fourth ventricle, ventriculus quartus (superior and posterior view)

Within the cavity of the fourth ventricle, In addition to the tela choroidea, there is the choroid plexus, plexus choroideus, and CEREBROSPINAL FLUID, liquor cerebrospinalis. Through the aforementioned openings, cerebrospinal fluid from the fourth ventricle freely enters the meningeal spaces, facilitating its normal Circulation. In inflammatory conditions of the Meninges (meningitis), circulation is impaired, and fluid accumulates in the ventricles, which can lead to Hydrocephalus.

Fig. 143 B. Diencephalon, diencephalon. View from the third ventricle.

Fourth ventricle, ventriculus quartus, cerebral aqueduct, and the third ventricle (sagittal section)