Axonal trajectories of masticatory motoneurons: a genu formation of axons of jaw-opening motoneurons in the cat.

Axonal courses of jaw-opening motoneurons were examined in the cat by applying horseradish peroxidase to the central cut end of the nerve branch which supplies the mylohyoid and/or the anterior digastric muscle. The axons of mylohyoid and anterior digastric motoneurons, which are located in the ventromedial division of the trigeminal motor nucleus, initially swing dorsally before running ventrolaterally to leave the pons; axons proceeding in the more rostral levels make turns in the more dorsomedial tegmental regions, and those running in the most rostral levels form a small genu in the region near the midline under the floor of the fourth ventricle.