Descending projections from the first three myelomeres.

By means of retrograde labeling with WGA-HRP, and anterograde Wallerian degeneration, the propriospinal connections of the first three cervical myelomeres of the rat have been studied. These cervical segments project to the caudal ones, at least as far as L4 (the last segment studied). These descending fibres arise from neurons located in the deeper laminae of the dorsal horn, mainly in laminae V-VII. They run bilaterally, but with ipsilateral predominance, principally in the cervical cord. The course of the descending fibres is predominantly intragriseal for the cervical segments, and in the pars dorsomedialis of the funiculus lateralis for the caudal segments. The laminae in what the grat part of these descending fibres project are, mainly, VII, V and VIII.