The spinal cord is surrounded and protected by three membranous layers called the spinal meninges:

Dura mater - tough and protective outermost layer that is formed by connective tissue containing a great amount of collagen and elastin fibers; it also covers the spinal nerve roots as they leave the intervertebral foramina, and it is composed of two layers - the outer is periosteal, while the inner is the meningeal layer;
Arachnoid mater - avascular spiderweb-like middle layer;
Pia mater - delicate and highly vascular innermost layer that provides blood supply to the spinal cord.

Meningeal spaces

All three meningeal layers do not connect with each other. Instead, between the adjacent layers and the vertebral canal walls are three gaps called meningeal spaces:

Epidural space - a space between the vertebral canal wall and the dura mater; it serves as an injection site for epidural anesthesia;
Subdural space - a gap between the dura mater and arachnoid mater;
Subarachnoid space - a space between the arachnoid mater and pia mater that contains cerebrospinal fluid.

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Spinal meninges and meningeal spaces