The spinal cord is bilaterally symmetrical. Right and left halves are separated by a ventral median fissure and a dorsal median sulcus continued by a dorsal median septum (the septum is replaced by a dorsal median fissure in the caudal half of the spinal cord). The dorsolateral suclus marks the site of entry of dorsal root fibers (not shown).

Internally, a central canal is surrounded by gray matter, in turn surrounded by white matter.