LOCALIZATION OF MOTO-NEURONS INNERVATING THE POSTERIOR BELLY OF THE DIGASTRIC MUSCLE - COMPARATIVE ANATOMICAL STUDY BY THE HRP METHOD

Motoneurons innervating the posterior belly of the digastric muscle were identified in the [rhesus] monkey, cat, dog, guinea pig and rat. After injections of horseradish peroxidase (HRP) into the posterior belly of the digastric muscle, 2 groups of HRP-labeled motoneurons were observed; the rostral group was seen as a small cluster of neurons in the lateral reticular area along the medial border of the descending root of the facial nerve, and the neurons of the caudal group were distributed among the ascending root fibers of the facial nerve. The distribution pattern of these neurons corresponded to that of the accessory facial nucleus neurons. The accessory facial nucleus was lacking in the rabbit which the posterior digastric (PD) muscle is non-existent.