Structure and innervation of the tracheal muscles of the white Pekin duck

The sternotrachealis muscle of the duck, Anas platyrhynchos, was examined by light and electron microscopy. Muscle fibres showed succinic dehydrogenase activity but a definite classification based on this was not possible. Muscle contained fibres with features similar to mammalian slow muscle. Neuromuscular junctions showed the presynaptic portion containing clear vesicles and mitochondria, whereas the postjunctional muscle membrane was smooth without any junctional folds.