Fig. 7. Spatial arrangement of the superficial extensor muscle, the deep extensor muscle and the stretch receptor. They are depicted on one side bisected along the midline. The dorsal nerve (dnr) continues to the third segmental nerve. A pair of thoracic stretch receptors is located under the lateral deep extensor muscle (DEM2). The superficial extensor muscles (SEM1 and SEM2) lie under the medial deep extensor muscle (DEM1). ANT, anterior; npm, nerve to deep extensor muscles; nsm, nerve to superficial extensor muscle; POST, posterior; SR, stretch receptor.