Pia mater

A) Functional unit of the nervous system
B) Most superficial and thickest meninx
C) The middle meninx
D) The meninx bound tightly to brain and spinal cord
E) Separates dura mater from periosteum

Pia Mater

The delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord.

Meninx

A layer of membrane covering the brain and spinal cord; refers to one of the meninges.

Periosteum

The periosteum is a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints.