Figure 1.

Simplified schematic diagram of the arm of an octopus showing the general three-dimensional arrangement of muscle fibres. A central mass of transverse muscle (TM) surrounds the axial nerve cord (AN) and extends peripherally in sheets called trabeculae (TR) to interdigitate with bundles of longitudinal muscle fibres (LM). Oblique muscle layers (OM), of both left and right handedness, are located on the lateral peripheries of the arm, separated by additional longitudinal muscle. SU, sucker; CM, circumferential muscle layer; TR, trabeculae—sheets of transverse muscle fibres that project through oblique and longitudinal muscle

(modified from¹⁶).