The Double Innervation of Muscles in the Clam (Mya Arenaria)

Two of the somatic muscles of the clam (Mya arenaria) are shown to receive a double motor innervation. The activity of one group of motor fibres, which yield action potentials of relatively great magnitude, is necessary to excite the muscle to complete and rapid contraction. The principal function of the second group which yield relatively small action potentials is to delay the relaxation of the muscle.