Trigeminal motoneurons with disparate dendritic geometry innervate different muscle groups in the frog.

Cobalt labelling revealed two, morphologically different types of neurons in the trigeminal motor nucleus innervating masticatory muscles and the levator bulbi muscle, respectively. As far as their neuronal morphology is concerned, levator bulbi motoneurons differed from all other motoneurons of the brainstem. They could not be found in lizards and rats; and the levator bulbi muscle was also absent in these animals. This motoneuron group is compared with the accessory abducens nucleus which innervates the retractor bulbi muscles, and is present only in animals which possess this muscle group.