Figure 14-2.

Organization of the Spinal Cord, Gray Matter, and White Matter.

A, White matter in the spinal cord is located peripherally and divided into dorsal, lateral, and ventral funiculi. As a general rule, dorsal funiculi (D) consist of ascending sensory axons, lateral funiculi (L) have a mixture of sensory and motor axons, and ventral funiculi consist of descending motor axons (V). Histologically, the right side is a mirror image of the left side. The areas labeled B and C and contained within the boxes correspond to the areas illustrated in B and C. B, Transverse section of spinal cord, ventral gray horn, horse. The cell bodies of large motor neurons (arrows) are those of lower motor neurons, and their axons extend in peripheral nerves to myoneural junctions that innervate skeletal muscle. H&E stain. C, Transverse section of spinal cord, ventral funiculus, horse. Because most axons course up and down the length of the spinal cord, in a transverse section, axons (arrows) are cut in cross section. They are surrounded by myelin sheaths whose lipid components are dissolved out during the preparation of paraffin-embedded sections, resulting in clear spaces that are an artifact. H&E stain. D, Efferent spinal nerve (longitudinal section shown here), transverse section of spinal cord, ventral funiculus, dog. Axons of lower motor neurons leave funiculi (F) and assemble as nerve rootlets (arrow) eventually forming peripheral nerves that innervate skeletal muscle. H&E stain. DGH, Dorsal gray horn; VGH, ventral gray horn.

(Courtesy Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)