On the rami intermedii of the spinal nerves and their equivalent offshoots

Distribution patterns of the nerves of supply to the intertransversarii posteriores cervicis, levatores costarum breves and intertransversarii laterales lumborum were carefully studied in nine body-halves of male human cadavers. Any of these muscles lie wegded in between the commencements of the dorsal and ventral primary rami of the spinal nerves. In the great majority of the cases the levatores costarum breves derived their nerve supply in the upper segments from both primary rami of the corresponding spinal nerves and in the lowest segments as the rami intermedii from the bifurcation of each spinal nerve into its primary rami. Both patterns of the nerve supply to the levatores costarum breves were turned into one another in the intervening segments. The intertransversarii posteriores cervicis of similar location to the levatores costarum breves in the thoracic region were regarded as the upper serial homologues of these muscles, because they were supplied by both primary rami of the spinal nerves, similarly the intertransversarii laterales lumborum, principally supplied by the rami intermedii of the spinal nerves, as the lower serial homologues of the same muscles. In view of location as well as mode of innervation it was proposed that the intertransversarii posteriores cervicis, levatores costarum breves and intertransversarii laterales lumborum should be grouped into the musculi intervertebrales laterales (abbrev. l) as the serially homologous muscles deriving innervation of an ambiguous character from both primary rami of the spinal nerves and therefore as the third muscle system more or less distinct from the musculi trunci dorsales (abbrev. D, Nishi) and ventrales (abbrev. V, Nishi) which are supplied alternatively by either of the primary rami of the spinal nerves.