Topographical representation of the peripheral nerve branches of the facial nucleus of the opossum: a study utilizing horseradish peroxidase.

The main facial nucleus of a marsupial, the North American opossum (Didelphis marsupialis virginiana), was subdivided into 6 portions by localizing HRP-positive neurons after injecting all muscles by each major peripheral motor branch of the facial nerve. In the medial lobe of this dumbbell-shaped nucleus the caudal auricular nerve, rostral auricular ramus and cervical ramus were represented dorsomedially, dorsolaterally and ventrally, respectively. The lateral lobe contained zygomatic ramus cells dorsomedially, marginal mandibular ramus cells ventromedially and buccal rami cells laterally. The cells supplying the caudal digastric muscle were in the accessory facial nucleus. Thus, even though the facial nucleus of the opossum lacks distinct ramal subdivisions in Nissl preparations, such are evident after HRP labeling.