ACTION OF THE HYPAXIAL MUSCLES DURING WALKING AND SWIMMING IN THE SALAMANDER DICAMPTODON-ENSATUS

Activity of the hypaxial muscles during walking and swimming was measu red in the salamander Dicamptodon ensatus. During walking, there was a ctivity on both sides of the trunk simultaneously. The obliquus extern us superficialis and profundus muscles were active on the side towards which the trunk was bending (flexing), while the obliquus internus an d transversalis muscles were active on the opposite side. In contrast, during swimming, all four of these muscles were active on the side of the trunk that was bending to become concave. These observations are consistent with the hypothesis that during terrestrial ambulation the obliquely oriented hypaxial muscles do not contribute to lateral bendi ng of the trunk or to horizontal propulsion, but to stabilization of t he trunk against long-axis torsion.