ABSTRACT. – The Octopus vulgaris arm is a muscular hydrostat mainly composed of closely packed incompressible muscle tissue and it has virtually unlimited degrees of freedom. The mechanical function of this special structure depends on the organization of muscle cells in the various muscle groups, the distribution of muscle and nerve cells along the arm and the connective tissue/muscle relation. Here we characterized the distribution of the muscle and the nerve cells along the arm. To do this, we used histological (Nissl staining and Sirius red connective staining) and immunohistochemical reactions (αActin, P0 and β III Tubulin) to identify cell types and estimate the ratio between the volumes occupied by the nervous and the muscle systems along the arm. We thus obtained a comprehensive view on the structural organization of sensory and motor components acting at different levels along an octopus arm. Given the increasing interest to bio-roboticists in highly flexible biological structures this study may provide important insights for the design of a biomimetic arm.