This section of the book is from "The Complete Herbalist" by Dr. O. Phelps Brown. Also available from Amazon: The Complete Herbalist: The People Their Own Physicians By The Use Of Nature's Remedies.
The spinal marrow is the medullary column included within the bones or vertebrae of the spinal column. It has three coverings: 1st, The dura mater, which is a white fibrous membrane, and forms the external; 2d, The arachnoid, a serous membrane, forming the middle covering. It is extremely thin and transparent; 3d, The pia mater, a cellular membrane, forming the immediate covering. It is very vascular, consisting almost entirely of vessels.