Evidence of a direct projection from the medial terminal nucleus of the accessory optic system to lobule IX of the cerebellar cortex in the tree shrew (Tupaia glis).

Injections of a wheat germ agglutinin-horseradish peroxidase conjugate were placed in representative areas of the cerebellar cortex of adult tree shrews. Retrogradely labeled cells were found in the medial terminal nucleus (MTN) of the accessory optic system (AOS) when ventral portions of the uvula were involved in the injection site. These labeled cells are small to medium sized and have round or oval somata and few primary dendrites. The AOS functions to stabilize the eyes and head in space. The present observations provide evidence of a direct projection from the MTN of the tree shrew AOS to regions of the posterior vermal cortex (ventral uvula) which, through interconnections with the vestibular nuclei, are involved in the regulation of eye movement.