Fig. 20. Mean electromyographic activity in the orbital and global layers of the human medial rectus muscle as influenced by eye position. Orbital layer fibers have generally higher activity than global layer fibers and are active over more of the oculomotor range. (Collins CC: The human oculomotor control system. In Lennerstrand G, Bach-y-Rita P [eds]: Basic Mechanisms of Ocular Motility and Their Clinical Implications, pp 145–180. New York: Pergamon, 1975.)