Action of the Hypaxial Muscles During Walking and Swimming in the Salamander Dicamptodon Ensatus

Activity of the hypaxial muscles during walking and swimming was measured in the salamander Dicamptodon ensatus. During walking, there was activity on both sides of the trunk simultaneously. The obliquus externus superficialis and profundus muscles were active on the side towards which the trunk was bending (flexing), while the obliquus internus and 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 bending of the trunk or to horizontal propulsion, but to stabilization of the trunk against long-axis torsion.