Descending pathways from the brain stem to the spinal cord in some reptiles. I. Origin.

In the present study of the origin of the pathways descending from the brain stem to the spinal cord has been investigated in the reptiles Testudo hermanni, Pseudemys scripta elegans, Tupinambis nigropunctatus and Python reticulatus. These reptiles, using highly different types of progression, have been selected, because fundamental variations in the organization of the central motor apparatus are to be expected. The origin of the descending pathways has been demonstrated by recording the occurrence of retrograde cell changes following hemicordotomies and by searching for labeled cells following injection into the spinal cord of the enzyme horseradish peroxidase. In the reptiles studies the presence of interstitiospinal, vestibulospinal and reticulospinal pathways could be demonstrated. A crossed rubrospinal tract has been shown in the turtles and in the lizard, but could not be demonstrated in the Python. The presence of a direct tectospinal pathway could not be shown.