Major reorganisations of trunk's musculature are involved in the evolutionary changes of locomotion. In primarily aquatic vertebrates, the axial musculature is ordered in serial, segmental units (myomeres). In amniotes, e.g. mammals, epaxial and hypaxial muscles have evolved into multi-segmental muscle tracts (transversospinalis & sacrospinalis). The present study was carried out to compare the structure and function of back muscles between bipedal humans and quadrupedal mammals. Microscopic dissections on two laboratory rats and Sihler's staining on ten juvenile animals uncover a segmental nervous supply of the most epaxial and hypaxial muscles. Particularly the multifidus and rotatores muscles are innervated without participation of the Plexus brachialis and lumbosacralis. During running on a treadmill a spatiotemporal activation pattern of both multifidus muscles were measured with 16 and 32 channel-matrix-electrodes at eight adult rats. The electrodes were positioned between the third and the fifth lumbar vertebrae. Subsequently the activation pattern was combined with gait characteristics and fibre typing of the muscles. A biphasic activation was observed in both multifidus muscles like in humans. This is astonishing in spite of the evolution of bipedal locomotion.