VENTRICULAR SYSTEM

 

The ventricles are the cavities located inside the encephalon. They are the remnants of the embryonic neural canal. They are lined by ependymal cells and contain the choroid plexuses and cerebrospinal fluid. The lateral ventricles (first and second ventricles) are located inside each cerebral hemisphere, the third ventricle is in the diencephalon, and the fourth ventricle is in the rhombencephalon. The small communication between the lateral ventricle and the third ventricle is the interventricular foramen[1]. The mesencephalic aqueduct[2] communicates the third and the fourth ventricles. Caudally, the fourth ventricle is continuous with the central canal[3] in the spinal cord.

 

According to Aristotle, the soul or human mind had three faculties: phantasia, anamnesis and mneme. In the late Middle Ages, it was accepted that these three powers resided in the ventricular system. Aristotle localized the phantasia or imagination in the lateral ventricles, the anamnesis or cognitatio in the third ventricle, and the mneme or memory in the fourth ventricle. To retain thoughts, these had to go through the mesencephalic aqueduct and be located on the walls of the fourth ventricle (Page 17 of "The pineal gland" by Bardasano Rubio, JL.  H. Blume Ed., 1978).

 

The lateral ventricles have an arcuate shape which corresponds to the shape of hemispheres. Each lateral ventricle can be divided into three parts: central part, rostral horn and temporal horn. The central part is bounded dorsally by the corpus callosum and ventrally by the caudate nucleus and the fornix. The rostral horn is the rostral extension of the lateral ventricle into the olfactory bulb. The temporal horn extends in the piriform lobe, bounded medially by the hippocampus.

 

The third ventricle surrounds the interthalamic adhesion. It continues into the infundibulum[4] through a neurohypophysary recess. The roof of the third ventricle is located between the interventricular foramen and choroidal fissure, and the pineal recess. The roof is covered by a double layer of trabecular pial tissue, the velum interpositum. The internal cerebral veins and the posterior choroidal arteries are located between the two layers of the velum.

 

The roof of the fourth ventricle is formed by a layer of ependymal cells and pia mater, called medullary velum (divided in rostral and caudal), and by the tela choroidea of the fourth ventricle. The rostral medullary velum is located between the rostral cerebellar pedunculi (left and right) and the lingula of the cerebellum. The caudal medullary velum is located between the caudal cerebellar peduncles (left and right) and gives rise to the tela choroidea of ​​the fourth ventricle. The tela choroidea extends up to the taenia of the fourth ventricle (it is the caudal limit of the roof of the fourth ventricle).

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The fourth ventricle opens into the subarachnoid space through the lateral apertures of the fourth ventricle[5] (located in the lateral recesses of the fourth ventricle). They are located caudally to the caudal cerebellar peduncles.

 

[1] Described in 1753 by the Scottish anatomist Alexander Monro

[2] Described in 1650 by Franciscus de la Boe Sylvius.

[3] This is a longitudinal canal localized in the spinal cord. It is enlarged at the caudal end, forming the terminal ventricle.

[4] From the Latin infundibulum, "funnel shape". It is the proximal part of the neurohypophysis.

[5] Named in 1863 by the German anatomist Hubert von Luschka.