Surgery of Spinal Column

The spinal cord itself is a cylinder slightly flattened from before backward. In the cervical region it is enlarged where the nerves forming the brachial plexus come off, while opposite the lower thoracic vertebrae the lumbar enlargement marks the region whence the lumbo-sacral nerves are derived. (See fig. 2.) Op posite the second lumbar vertebra the cylindrical cord becomes pointed and forms the conus medullaris, from the apex of which a glistening membranous thread runs down among the nerves which form the cauda equina, and, after blending with the ter mination of the dural sheath, is attached to the back of the coccyx.

Details of Structure.

In a transverse section of the cord (see fig. 3) two median fissures are seen; the antero-median is wide, and reaches about a third of the way along the antero posterior diameter of the cord ; it is lined by the pia mater and, in front, lies the single anterior spinal artery.

The postero-median fissure is much deeper and narrower, and has no reflection of the pia mater into it. Where the posterior nerve roots emerge is a depression which is called the postero lateral fissure, while between this and the postero-median a slight groove is seen in the cervical region, the paramedian fissure (see also fig. 2). The anterior nerve roots do not emerge from a

definite fissure.

The spinal cord, like the brain, consists of grey and white matter, but, as there is here no representative of the cortical grey matter of the brain, the white matter entirely surrounds the grey. In section the grey matter has the form of an H, the cross bar forming the grey commissure. In the middle of this the central canal can just be made out by the naked eye (see fig. 4). The anterior limbs of the H form the anterior or ventral cornua, while the posterior, which in the greater part of the cord are longer and thinner, are the posterior or dorsal cornua. At the tips of the latter is a lighter-coloured cap known as the substantia gelatinosa Rolandi. On each side of the H is a slighter projection, the lateral cornu, best marked in the thoracic region (see fig. 4).

The grey matter has different appearances in different regions of the cord, and in the cervical and lumbar enlargements, where the nerves to the limbs come off, the anterior horns are broadened (see fig. 4).

Histologically the grey matter is made up of neuroglia, medul lated and non-medullated nerve fibres, and nerve cells (see