Somatotopic organization of the axons innervating the superior rectus muscle in the oculomotor nerve of the rat.

It has long been known that the pupillomotor fibers have a localized course in the dorsomedial periphery through the subarachnoid portion of the oculomotor nerve. However we do not have detailed knowledge about the organization of the fibers innervating individual extraocular muscles. This subject is of clinical importance for locating the site of lesions in patients with partial oculomotor nerve palsies. In this study the peripheral course of the axons innervating the superior rectus muscle were studied in the subarachnoid portion of the oculomotor nerve of the rat by making multiple injections of horseradish peroxidase solution into the muscle and reacting the nerve with tetramethylbenzidine as a chromogen. Coronal sections of the nerve showed that the axons innervating the superior rectus muscle were localized in the dorsal part of the nerve. Within the precavernous portion these axons showed a wider distribution invading dorsomedial and dorsolateral parts of the nerve.