The white matter of the spinal cord is divided into strands, 3 on each side of the mean line:
1/ the posterior cord located between the middle line and the entry of the hind roots into the spinal cord
2/ the side string located between the entry of the hind-roots and the exit of the fore-roots
3/ the front string that lies between the exit of the front roots and the middle furrow.
The white matter gradually decreases in quantity in a descending direction. The explanation is simple: At the top of the dorsal wall, all upward and downward threads are gathered in the cross section. Further down, some of the downward threads have already turned into the grey matter where they end, and upward threads from above-ground segments are of course not included.