Motoneurons differ in size and peripheral target in the trigeminal and facial nuclear complex of the frog

The cobalt labelling technique was applied to different branches of the frog trigeminal and facial nerves and the representation of muscle supplied by these nerves were studied. (1) The levator bulbi muscle is innervated by a small group of neurons localised in its rostromedial part of the trigeminal motor nucleus (nV). (2) The jaw closer muscles are represented in the rostral two thirds of the nV. (3) Muscles of the floor of the mouth, which contribute to the jaw opening, and the depressor mandibulae muscle are innervated from the caudal one third of the nV and from the facial motor nucleus, respectively. There were distinct differences in the shape and size of perikarya innervating these three functionally different muscle groups.