Bilateral innervation of the superior oblique muscle by the trochlear nucleus

Trochlear motoneurons and their axons were labeled by applying horseradish peroxidase (HRP) solution to the transected trochlear nerve stump in the orbit of cats and rabbits. Although almost all labeled neurons were on the contralateral trochlear nucleus, about 5% of them and their axons were on the ipsilateral side. These findings confirmed that the superior oblique muscle was innervated partially by a small number of ipsilateral trochlear nucleus.