leptomeninges

The arachnoid & pia mater considered together like the parietal & visceral layers of a serous membrane or bursa. Although separated by the subarachnoid space, they are connected via the arachnoid trabeculae & becomes continuous where the nerves & filum terminale exit the subarachnoid space.

Specific

arachnoid pia mater

References

Stedman's Medical Dictionary 26th ed, Williams & Wilkins, Baltimore, 1995