Spinal

{spi;-nal)\j;pina, spine], I. Pertaining to the spine. 2. Pertaining to the S. cord. S. Acce ory Nerve. See Nerves, Table of. S. Canal. See Canal, Vertebral. S. Column, the vertebral column, composed of vertebrae, intervertebral cartilages, and ligaments. S. Cord, the neural structure occupying the vertebral canal and extending from the atlas to the first lumbar vertebra, and terminating in the filum term in ale. It is covered by the S. membranes (the pia mater, arachnoid, and dura mater) and is divided into symmetric halves by the anterior and posterior median fi ures. These halves are joined together by the anterior white commi ure and the gray commi ure. In the middle of the latter is the central canal, a continuation of the ventricular cavities of the brain. Each half of the S. cord consists of an internal ma of gray matter and an outer covering of white matter. The former is subdivided into the anterior and posterior horns, which are made up of ganglion -cells, nerve-fibers, and delicate fibrillae, and a modified neuroglia, the subs tanti a gelati nos a. The white matter is divided by the two gray horns into three columns: the anterior, lateral, and posterior. These are again subdivided into distinct physiologic tracts. Thus the anterior column includes the direct pyramidal tract (Turck’s column) and the anterior ground-bundle, or anterior radicular zone, which is continuous with the adjacent part of the lateral column. In the latter the following tracts are distinguished: the cro ed pyramidal, direct cerebellar, anterolateral (Gowers’ tract), and mixed lateral tract. The posterior column contains the posteromedian tract (Goll’s column) and the posterolateral or posteroexternal tract (Burdach’s column). The spinal cord is the conductor of impulses from and to the brain, as well as a center for reflex acts. S. Epilepsy. See Epilepsy. S. Irritation, a form of neurasthenia characterized by pain in the back, tenderne along the spines of the vertebrae, fatigue on slight exertion, and occasionally numbne and tingling in the limb S. Nerves, the 31 pairs of nerves arising from the S. cord, and grouped into 8 Cervical, 12 Dorsal, 5 Lumbar, 5 Sacral, I Coccygeal. Each arises by two roots, a dorsal (gangliated) root and a ventral (anterior, non gangliated) root. On the dorsal root is the spinal ganglion. Beyond the ganglion the two roots unite to form, in the spinal canal, the mixed trunk of a spinal nerve. The anterior roots supply efferent fibers to all the voluntary muscles of the trunk and extremities, to the smooth muscular fibers of the bladder, ureter, uterus, etc., vasomotor, inhibitory, secretory, and trophic fibers. The posterior roots carry afferent impulses. 593