SPINAL CORD

the elongated cylindrical part of the central nervous system, enclosed in the spine, or backbone. It is usually about 16 in. in length, and does not nearly fill the spinal canal, its investing membranes being separated from the bony wall by areolar ti ue and a plexus of veins, as well as by cerebro-spinal fluid, while in the adult it does not reach lower than the first lumbar vertebra, where it ee na a slender thread of grey matter. e spinal cord is a flattened cylinder, with a deep longitudinal furrow or fi ure on both the anterior and the posterior aspects. In transverse section the cord is seen to consist of white and grey matter, of which the white lies externally, and constitutes the greater part. The grey matter is arranged somewhat in the shape of a crescent in each half of the cord, the two crescents being united near their middle by grey matter which pa es acro the commi ure. Both the white and the grey matter contain a supporting ti ue known as neuroglia, which consists of elastic fibres and nucleated cells. The spinal cord is supplied with a large number of blood- ~ ve els, and the blood-ve els and ganglion cells are surrounded by lymph spaces. The cord is enveloped in three membranes—the dura mater, the arachnoid membrane, and the pia mater— which are composed of fibrous connective ti ue and endothelium. The white medullated fibres which join the anterior pyramids of the medulla oblong at a decu ate almost entirely before entering the spinal cord, and it is owing to this that hemiplegic paralysis so often affects the side of the body opposite to that on which the lesion is. The nerve filaments of the white matter depend for their vitality upon the cells from which they spring, and should heemorrhage or other lesion destroy the cell in the cortex cerebri, the whole filament undergoes speedy degeneration. Should the filament be severed at any point, the portion situated distally from the cell degenerates in the same way. Destruction of the ganglionic cells of the cord is followed by degeneration of the motor fibres of the corresponding spinal nerve, and the muscles are also dependent upon these cells for their nutrition. Throughout the entire length of the spinal cord sensory fibres cro from one side to the other. A unilateral lesion of the spinal cord, therefore, produces motor paralysis on the same side as the lesion, along with sensory paralysis on the opposite side, the paralysis in each case being only below the seat of the lesion. The column of Goll, which lies in the posterior column - close alongside the posterior median fi ure, seems to convey the sensation of touch and the muscular sense. See under Nervous System,