Mesencephalic flexture12/26/2023 Overall, the final tentorium cerebelli corresponded to the regressed plica ventralis, while the parasellar area originated from the base of the plica and other tissues along the ventral aspects of the basisphenoid and basioccipital.Īfter the intracranial venous-drainage route is switched from the vena capitis prima (VCP) to the transverse sinus, the cavernous sinus is considered to develop from a connecting part of the VCP with the ophthalmic vein (OPV). The falx cerebri seemed to develop from the tongue-like folds. Up to 9-10 weeks, the lateral mesenchymal condensations became tongue-like folds i.e., the primitive form of the tentorium cerebelli, while the membranous meninx became the diaphragma sellae. Notably, the topographical anatomy of the oculomotor, trochlear and trigeminal nerves did not change: the oculomotor nerve ran along the rostral aspect of the membranous meninx, the trigeminal nerve ran along the caudal side of the lateral mesenchymal condensation, and the trochlear nerve remained embedded in the lateral condensation. Subsequently, the plica ventralis evolved into 3 parts: bilateral lateral mesenchymal condensations and a primitive membranous meninx extending between. In the loose tissues of the plica, the first meninx appeared as a narrow membrane along the oculomotor nerve at 7-8 weeks. We histologically examined paraffin-embedded sections from 18 human embryos and fetuses at 6-12 weeks of gestation. A distinct mesenchymal structure, the so-called plica ventralis encephali, is sandwiched by the fetal mesencephalic flexure. Development of the meninges in and around the plica ventralis encephali has not been well documented.
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