Spinal cord. Light micrograph of a cross-section through a mammalian spinal cord. The central canal (white) is surrounded by dorsal (light brown) and ventral horns (dark brown), which consist of grey matter made up of nerve cell bodies and their connections (ganglia). Outside the grey matter is the white matter (black-white), which consists mainly of long nerve cell axons which run up and down the spinal cord. The outer layers are the outer membranes (meninges) that protect and nourish the spinal cord. Magnification: x100 when printed at 10 centimetres across.