The thecal sac, or dural sac, is the membranous sheath of dura mater that surrounds the spinal cord and the cauda equina. The thecal sac contains the cerebrospinal fluid in which the spinal cord 'floats'.
Is the dura matter ectoderm? I know neural crest and such is ectoderm. But the meninges, in particular the dura, where do they come from?