Central location of the motoneurons supplying the thyrohyoid and the geniohyoid muscles as demonstrated by horseradish peroxidase method.

After HRP injection into the geniohyoid muscle labeled neurons were found in the ventral part of the hypoglossal nucleus, extending in the rostral two-thirds (about) of this nucleus. After HRP injection in to the thyrohyoid muscle, the labeled neurons were identified in the lateral part of the caudal one-third (about) of the hypoglossal nucleus and in the dorsomedial part of the ventral horn of C1.