The reticular premotor neurons of the jaw muscle motor nuclei in the mallard (Anas platyrhynchos L.).

The trigeminal and facial motor nuclei in the mallard comprise several subnuclei which innervate tongue, jaw and other head muscles. The premotor cells of the subnuclei innervating jaw muscles are distributed in two longitudinal cell columns within the parvocellular reticular formation (RPc). The ventromedial part of RPc contains cells projecting to subnuclei innervating either jaw-closer muscles or jaw-opener muscles. In the dorsolateral part of RPc three subdivisions may be recognized: a rostral part which projects to two trigeminal subnuclei innervating jaw-closer muscles, an intermediate part which does not serve as premotor area for any of the jaw motor subnuclei and a caudal part of RPcdl which projects to the trigeminal and facial motor subnuclei innervating jaw-opener muscles. Exteroceptive information from mechanoreceptors in the beak reaches all three parts of RPCdl. Muscle spindles in jaw-closer muscles may influence the activity of premotor cells of jaw-opener muscles through their projection upon the caudal part of RPcdl.