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Medical Definition of Septum pellucidum
1. A thin plate of brain tissue, containing nerve cells and numerous nerve fibres, that is stretched like a flat, vertical sheet between the column and body of fornix below, the corpus callosum above and anteriorly; it is usually fused in the median plane with its partner on the opposite side so as to form a thin, median partition between the left and right frontal horn of the lateral ventricles; in less than 10% of humans there is a blind, slitlike, fluid-filled space between the two transparent septa, the cavity of septum pellucidum. The transparent septum is continuous ventralward through the interval between the corpus callosum and the anterior commissure with the precommissural septum and subcallosal gyrus. See: cavity of septum pellucidum, septal area. Synonym: septum pellucidum, septum lucidum. (05 Mar 2000)