Cisterna chiasmatis (Figs. 14,22, 43, and 45 to 48)

Abstract

Cisterna chiasmatis is the center of the upper basal cisterns. The cisternal barrier area between Cisterna chiasmatis and Cisterna laminae terminalis is located between Chiasma and the outer arachnoid membrane. The barrier between Cisterna chiasmatis and Cisterna valleculae is the lateral margin of N. opticus — Chiasma — Tractus opt. and the medial segment of Cisterna cruralis, as shown in Fig. 14. These areas predominantly consist of arachnoid membranes interrupted by multiple gaps and trabecula, as described by Key and Retzius (1876). The lateral wall separates Cisterna chiasmatis and Cisterna valleculae (carotid cistern). The posterior wall is divided into two segments: One segment which separates Cisterna chiasmatis from Pars profunda of Cisterna interpeduncularis and the other which separates Cisterna chiasmatis from Pars superficialis, as shown in Fig. 22. Only the second part is identical to the well defined Liliequist’s membrane and is located below the trabecular structured border of Cisterna chiasmatis and Pars profunda of Cisterna interpeduncularis.