What is the X in X-mas?
plural, 1610s, "the three membranes enveloping the brain and spinal cord," from Middle French meninges (1530s) or directly from medical Latin, plural of meninx, from Greek meninx (see meningitis).
meninx me·ninx (mē'nĭngks)n. pl. me·nin·ges (mə-nĭn'jēz) A membrane, especially one of the three membranes enclosing the brain and spinal cord.
The membranes that surround the brain and spinal cord.