The oculomotor (III) nerve divides into superior and inferior divisions, usually at the superior orbital fissure. The superior division or ramus supplies the superior rectus and levator palpebrae superioris muscles; the inferior division or ramus supplies medial rectus, inferior rectus and inferior oblique muscles. Isolated dysfunction of these muscular groups allows diagnosis of a divisional palsy and suggests pathology at the superior orbital fissure or anterior cavernous sinus. However, occasionally this division may occur more proximally, at the fascicular level (i.e., within the midbrain) or within the subarachnoid space, giving a false-localizing divisional palsy. This may reflect the topographic arrangement of axons within the oculomotor nerve.
Larner AJ. Proximal superior division oculomotor nerve palsy from metastatic subarachnoid infiltration Journal of Neurology 2002; 249: 343-344