Answer:
dura mater
Step-by-step explanation:
The brain has three membranes between the bone, and the brain, the meninges: dura mater, arachnoid mater and pia mater.
Dura mater is the most external one, closest to the skull.
Arachnoid mater is the one in the middle. Looks like a spider-web, and that's why the name.
Pia mater is in touch with the brain and spinal cord, this is the thinner one.