Is the thecal sac ectoderm? 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?

The _dura mater_ is formed by the mesoderm. The mesoderm is the middle layer of the early trilaminar embryo. The three germ layers are the ectoderm, mesoderm and endoderm, formed by gastrulation. The middle germ layer forms **connective tissues** and **muscle** throughout the body, with the exception of the head region, where some of these structures have a neural crest (ectoderm) origin. Connective tissues include cartilage, bone, blood, blood vessel endothelium and dermis, but also the _dura mater_. The muscles include cardiac, skeletal and smooth muscle (fig. 1).

![germ layers](
Fig. 1. Germ layers. Source: UNSW

**Source**
**-** UNSW