In cross sections of the spinal cord, white matter is peripheral and gray matter is internal and has the general shape of letter H. In the center is an opening, the central canal, which develops from the lumen of the embryonic neural tube. The canal is continuous with the ventricles of the brain, contains CSF, and is lined by ependymal cells. The gray matter forms the anterior horns, which contain motor neurons whose axons make up the ventral roots of spinal nerves, and the posterior horns, which receive sensory fibers from neurons in the spinal (dorsal root) ganglia. Spinal cord neurons are large and multipolar, especially the motor neurons in the anterior horns. A cross section of H & E stained spinal cord shows the transition between white matter and gray matter. The gray matter has many glial cells, neuronal cell bodies, and neuropil; white matter also contains glia but consists mainly of axons whose myelin sheaths were lost during preparation, leaving round empty spaces. Each such space surrounds a dark-stained spot that is a small section of the axon. Mescher, A.L. (2013). Junqueira’s Basic Histology (13 ed.). McGraw Hill Education.