an architectural scheme used to classify the structure of the spinal cord, based on the features of the neurons in different regions of the gray substance. It consists of nine laminae (layers), designated by the roman numerals I–IX, that extend throughout the cord, roughly paralleling the dorsal and ventral columns of the gray substance, and a tenth region (area X, called also lamina X) that surrounds the central canal. in a cross section of the spinal cord at approximately the level of the seventh cervical vertebra (C7).