Fig. 1.

Transverse section through the octopus arm.A, The intrinsic musculature of the arm is an array of densely packed muscle fibers organized in three main directions: longitudinal fibers (L), transverse fibers (T), and oblique fibers (O). N, Axial nerve cord in the center of the arm: SRM, muscles of the sucking rings on the ventral side. Dorsal side is up. B, Transverse section at the level of an EMG electrode showing the stainless steel wire position (white arrows) inside the intrinsic muscle.