title: Compartmental Innervation of the Superior Oblique Muscle in Mammals.
abstract: OBJECTIVE
  Intramuscular innervation of mammalian horizontal rectus extraocular muscles (EOMs) is compartmental. We sought evidence of similar compartmental innervation of the superior oblique (SO) muscle.
  
  
  METHODS
  Three fresh bovine orbits and one human orbit were dissected to trace continuity of SO muscle and tendon fibers to the scleral insertions. Whole orbits were also obtained from four humans (two adults, a 17-month-old child, and a 33-week stillborn fetus), two rhesus monkeys, one rabbit, and one cow. Orbits were formalin fixed, embedded whole in paraffin, serially sectioned in the coronal plane at 10-μm thickness, and stained with Masson trichrome. Extraocular muscle fibers and branches of the trochlear nerve (CN4) were traced in serial sections and reconstructed in three dimensions.
  
  
  RESULTS
  In the human, the lateral SO belly is in continuity with tendon fibers inserting more posteriorly on the sclera for infraducting mechanical advantage, while the medial belly is continuous with anteriorly inserting fibers having mechanical advantage for incycloduction. Fibers in the monkey superior SO insert more posteriorly on the sclera to favor infraduction, while the inferior portion inserts more anteriorly to favor incycloduction. In all species, CN4 bifurcates prior to penetrating the SO belly. Each branch innervates a nonoverlapping compartment of EOM fibers, consisting of medial and lateral compartments in humans and monkeys, and superior and inferior compartments in cows and rabbits.
  
  
  CONCLUSIONS
  The SO muscle of humans and other mammals is compartmentally innervated in a manner that could permit separate CN4 branches to selectively influence vertical versus torsional action.
authors.affiliation: Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, California, United States 2Biomedical Engineering Interdepartmental Program, University of California, Los Angeles, California, United States.
authors.forename: Alan
authors.initials: A
authors.lastname: Le
authors.affiliation: Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, California, United States.
authors.forename: Vadims
authors.initials: V
authors.lastname: Poukens
authors.affiliation: Department of Ophthalmology, Johns Hopkins University, Baltimore, Maryland, United States.
authors.forename: Howard
authors.initials: H
authors.lastname: Ying
authors.affiliation: Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, California, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rootman
authors.affiliation: Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, California, United States.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Goldberg
authors.affiliation: Department of Ophthalmology, Stein Eye Institute, University of California, Los Angeles, California, United States 2Biomedical Engineering Interdepartmental Program, University of California, Los Angeles, California, United States 4Neuroscience Interdepar.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
mesh_terms: D000328:Adult; D000818:Animals; D002102:Cadaver; D002417:Cattle; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D009801:Oculomotor Muscles / Q000294:innervation; D009882:Ophthalmic Nerve / Q000033:anatomy & histology*; D009915:Orbit / Q000294:innervation; D011817:Rabbits