1. On (or outside) the dura mater. [Usage note: epidural and extradural are nearly synonymous, with the exception that epidural implies immediate proximity to the dura mater, and extradural may be unconnected with it.]
The information shown above for epidural is provided by Stedman's.
* Stedman's, part of Lippincott Williams & Wilkins, provide a comprehensive line of health-science publications for healthcare professionals and medical students.