meninx /ˈmiːnɪŋks, ˈmɛnɪŋks/;[3] from Ancient Greek μῆνιγξ (mêninx) 'membrane')[4] are the three membranes that envelop the brain and spinal cord.

[5] The dura mater (Latin: tough mother),[6][a] is a thick, durable membrane, closest to the skull and vertebrae.

This thin, transparent membrane is composed of fibrous tissue and, like the pia mater, has an outer layer of tightly packed flat cells, forming the arachnoid barrier.

It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid.

The subarachnoid lymphatic-like membrane (SLYM) is a possible fourth meningeal layer that was proposed in 2023 in the brain of humans and mice.

[16] In the early 1900s, Giuseppe Sterzi, an Italian anatomist, carried out comparative studies on the meninges from the lancelet to the human.

From the mesenchyme surrounding the neural tube, only a single leaflet forms the primitive meninx.

In the following phylogenetic and ontogenetic stages, the latter divides into an internal leaflet: the secondary meninx, and into an external one: the dura mater.

In the same animals, Sterzi demonstrated that, while in the spinal medulla the dura keeps its identity, in the skull it fuses with the periosteum.