The projections from the ophthalmic, maxillary, and mandibular parts of the trigeminal ganglion upon the principal sensory trigeminal nucleus (PrV) in the mallard have been studied with the Fink-Heimer I method. PrV is a large nucleus subdivided in cell groups by layers of fibers. The orientation of the dentritic arborizations differs in the different parts of the nucleus. A dorso-caudal cell group sIX is an exclusive glossopharyngeal terminal field. A second, caudo-ventral projections area of NIX also receives trigeminal afferents. A small n. supratrigeminalis lies medial to PrV in the pathway of the mesencephalic trigeminal root. This nucleus seems to be part of the proprioceptive trigeminal system. The rostralmost part of PrV receives ophthalmic projections, the caudalmost part receives mandibular projections, the maxillary area being intermediate. Taking the stereotaxic plane of the mallard atlas (Zweers, '71) into account, it can be concluded that the situation is essentially not different from that in the pigeon and from the situation described for mammals.