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Other Terms: Medulla spinalis, Moelle spinale, Rückenmark, Médula espinal
The spinal cord occupies the upper two-thirds of the vertebral canal, and is a direct continuation of the medulla oblongata. It extends from the lower border of the foramen magnum to the level of the upper border of the body of the second lumbar vertebra. Near its termination, it assumes a conical shape, the conus medullaris, and terminates in a slender thread, the filum terminale. In the fetus, up to the third month, the cord extends the entire length of the spinal canal. But due to the more rapid and continuous growth of the vertebral column, the cord soon ceases to occupy the entire canal. At birth it extends only to the third lumbar vertebra. The length of the spinal cord in the adult varies from forty to fifty centimeters. The average weight is about 28 grams. It is a somewhat flattened cylinder, wider in its transverse diameter. However, in the thoracic region, it is almost cylindrical. Lodged as it is in the spinal canal, it follows the curves of the spinal column. It presents a cervical enlargement between the third cervical and the second thoracic vertebra, and a lumbar enlargement between the ninth thoracic and first lumbar vertebrae. The former enlargement is widest opposite the sixth cervical, and the latter opposite the twelfth thoracic vertebra. These enlargements occur where the large nerves are given off to supply the extremities. The membranes, or meninges, of the spinal cord are the dura mater, the arachnoid, and the pia mater. They are continuous with the corresponding membranes of the brain, and hold the same relation to each other as those of the brain.