Bilateral innervation of syringeal muscles by the hypoglossal nucleus in the jungle crow (Corvus macrorhynchos).

Bird vocalizations are produced by contractions of syringeal muscles, which are controlled by the hypoglossal nucleus. In oscines, syringeal muscles are controlled by the hypoglossal nucleus ipsilaterally, whereas syringeal innervation is bilateral in non-oscines. We have determined the course of hypoglossal nerves in the jungle crow Corvus macrorhynchos. Our results indicate a cross-over of the hypoglossal nerve from the left side to the right side on the trachea 7 mm rostral to the Musculus sternotrachealis. We also investigated the innervation of the syringeal muscles of jungle crows from the hypoglossal nucleus using the horseradish peroxidase (HRP) method. After HRP was injected into the syringeal muscles on each side, HRP-labeled cells were found bilaterally in the hypoglossal nerve. These results suggest that the syringeal muscles of jungle crows are innervated bilaterally from the hypoglossal nucleus, although these birds are categorized as oscines.