Architecture of cerebellomedullary cistern structures during foetal period.

Structures of arachnoid in posterior cranial fossa have been examined during prenatal period. 100 foetuses were examined within IV up to VII month with CRL from 130 mm to 220 mm. Cuts were performed with especially constructed device what enabled ideal cross-section without disturbing of structures of arachnoid of dura mater. Image acquisition was done with the help of digital camera. The very fine structures spanned between posterior cranial fossa and cerebellum and brain stem were made visible. They are characteristics for prenatal period solely. This construction enables light weight elasticity and probably it increases strength as well as stability of circulation. Cross-section of observed structures has geometry of tangent circles with different diameters. Described structure fills entirely space situated outside of holes of posterior cranial fossa. It has the form of lattice with longitudinal meshes. Such structures were formed for foetuses with CRL - 140 mm and this was maintained up to VII month with CRL - 230 mm. Geometry of observed structures resembles Apollonian circles. There are many variations due to individual differences of foetuses. In turn power exponent for Applonian circles seems to be much more general.