The middle of the human brain contains a membrane structure that separates the two halves of the cerebrum. This membrane, a septum, so fine that it allows light to pass through it, it is almost translucent; pel-lucid, named in Latin; the septum pel lucidum, i.e. the dividing wall that is translucent.
Absence of the septum pellucidum occurs in certain congenital conditions and because the septum is involved with formation of the tracts concerning vision, it is often associated with blindness, and incidentally many other neurological problems.
I have included the X-ray of a newborn baby with congenital absence of this structure as well as absence of other brain structures. The Chest X-ray itself was normal.
The image consists of two base images; a red flower, colour inverted, and a layer of rusty iron is subtracted. Light (lux in Latin) is provided by a picture of a candle overlaid to give focus to the image.