Relation of medullary motor nuclei to nerves supplying the vocal tract of the budgerigar (Melopsittacus undulatus).

The locations of brainstem motor nuclei supplying efferents to organs of the vocal tract of the budgerigar (Melopsittacus undulatus) were determined as a first step in describing brain pathways for vocal control in this species. We identified four major nerves supplying the muscles of the syrinx, larynx, and tongue, and separately treated each of these with horseradish peroxidase. Nerves supplying efferents to the larynx and tongue arise from ipsilateral cells in the nucleus ambiguus and hypoglossal nucleus, respectively. Each right and left half of the syrinx is supplied by both right and left halves of the hypoglossal nucleus, via axons crossing in the common anastomosis of the tracheosyringeal nerves. This bilateral innervation of the syrinx will allow testing for central asymmetries of dominance for vocal control in the absence of any underlying anatomical laterality in the periphery.