septum pel·lu·ci·dum 
(pə-lsĭ-dəm)
(pə-lsĭ-dəm)n. pl. septa pel·lu·ci·da (-də)
A thin membrane of nervous tissue that forms the medial wall of the lateral ventricles in the brain.
[New Latin sēptum pellūcidum : sēptum, septum + Latin pellūcidum, neuter of pellūcidus, transparent.]