organ cavitated compound organ spinal cord Part of the central nervous system located in the vertebral canal continuous with and caudal to the brain; demarcated from brain by plane of foramen magnum. It is composed of an inner core of gray matter in which nerve cells predominate, and an outer layer of white matter in which myelinated nerve fibers predominate, and surrounds the central canal. (CUMBO) spinal cord ectoderm-derived structure structure with developmental contribution from neural crest