Figure 68: The Course of the 4th (IV) Nerve

The 4th nucleus lies at the ventral border of the periaqueductal gray matter, at the level of the inferior colliculus. The fascicles exit the nucleus dorsally and decussate at the anterior medullary velum (anterior floor of the fourth ventricle), and then exit the brainstem dorsally. The peripheral portion of the 4th nerve (left 4th nerve originated in the right 4th nucleus and vice versa) runs laterally around the upper pons and then passes between the superior cerebellar and posterior cerebral arteries before reaching the prepontine cistern and then the cavernous sinus where it is located laterally. The 4th nerve travels through the superior orbital fissure and continues above the annulus of Zinn to then innervate the superior oblique muscle.