Background: The boundary separating the posterior columns of the spinal cord is formed by the lateral margins of the neural groove approximating to form the neural canal. In anatomy texts this line is usually drawn as continuous, uniform, centered, and straight. It is universally termed posterior or dorsal, median "septum".
Methods: Sections from the cervical and lumbar enlargements and the mid-thoracic region were examined from 35 human autopsy specimens from 20 weeks gestation to 70 years with no history of spinal cord disease or trauma. They were stained with Masson's trichrome, and by immunohistochemistry for collagen types 1 and 4, and for glial fibrillary acidic protein (GFAP).
Results: One or more variations were found in the position character, shape, or extent of the line at one or more levels in every case. There was no midline staining for collagen other than that associated with blood vessels. There is intense immunoreactivity for GFAP from 20 weeks gestation to 35 weeks diminishing thereafter. When the posterior columns are separated the "septum" divides.
Conclusion: In the absence of any collagen this line of separation is more akin to a raphé than a septum. Inasmuch as there is an immediately adjacent subarachnoid posterior median septum it would be advantageous to re-name this intraspinal structure "dorsal" or "posterior" median raphé.