EXTERNAL CONFIGURATION.
The anterior or ventral surface of the spinal cord is cleft in the mid-line by a deep longitudinal furrow, the fissura mediana anterior; the posterior or dorsal surface is modelled by a superficial dinal groove, the sulcus medianus posterior. By means of these two rows the spinal cord is divided into symmetrical halves. Lateral to the posterior median sulcus, in each half runs the sulcus lateralis posterior, along which the terior root-bundles enter.
Lateral to the anterior median fissure, on each side extends the sulcus lateralis anterior, which is not a continuous furrow, unless the emerging anterior root-fibres are torn away. In the upper thoracic and the cervical region, an additional delicate tudinal groove, the sulcus intermedius posterior, is distinguishable between the median and lateral posterior sulci. The anterior root-fibres that emerge along the anterior lateral sulcus form individual bundles, the radices anteriores, rated from one another by intervals. The posterior fibres, which enter along the posterior lateral sulcus in an unbroken row, likewise form outwardly converging bundles, the radices posteriores. Each pair of anterior and posterior root-bundles passes to a defi nite foramen intervertebrale (Fig. 93). Here, the posterior root presents a small fusiform swelling, the ganglion spinale, and then unites in its fur ther course with the corresponding anterior root, thereby forming the spinal nerve, which latter divides into an anterior and posterior division.
The emerging root-bundles run not only outward, but at the same time caudalward, and, indeed, the more so the nearer to the caudal end of the spinal cord they emerge. In the lumbar region, the course of the nerve-roots within the vertebral canal is nearly parallel with the long axis of the cord, so that the conus medullaris and the filum terminale lie in the midst of a generous bundle of nerve-roots, which, on account of the supposed resemblance to a horse's tail, is designated the cauda equina.
By means of the longitudinal furrows, the spinal cord is subdivided into the following columns : The funiculus anterior, between the anterior median fissure and the anterior lateral sulcus ; The funiculus lateralis, between the anterior and posterior lateral sulci ; The funiculus posterior, between the posterior median fissure and the posterior lateral sulcus. The posterior column is separated by the sulcus intermedius posterior into a medial and a lateral division, the medial one being known as the fasciculus gracilis, or Goll' s column, and the lateral one as the fasciculus cuneatus, or Burdach's column.