The innervation of the monkey accessory lateral rectus muscle.
The source and pattern of innervation of the accessory lateral rectus muscle has been re-investigated in 3 Macaca fascicularis monkeys by means of a tracing method employing [125I] wheat germ agglutinin and a morphological analysis of the myo-neuronal junctions. The present findings suggest that this muscle is composed of exclusively singly innervated fibers and that its motoneurons are situated in the accessory abducens nucleus. This is in contrast to a previous study, where the monkey accessory lateral rectus was found to be composed of singly and multiply innervated fibers and to be innervated by a group of motoneurons lying within principle and accessory abducens nucleus. It is concluded that the monkey accessory lateral rectus reflects in principle the organization of the retractor bulbi of other vertebrates, although this muscle is gradually vanishing in primate evolution and remains vestigial in the macaque monkey. The absence of comparable motor units in man is more likely to mean an actual loss of structure and function than their integration into the lateral rectus system.
D000818:Animals; D001370:Axonal Transport; D007457:Iodine Radioisotopes; D037102:Lectins; D008251:Macaca / Q000502:physiology*; D008252:Macaca fascicularis / Q000502:physiology*; D009045:Motor Endplate / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009132:Muscles / Q000294:innervation*; D014909:Wheat Germ Agglutinins
D007457:Iodine Radioisotopes; D037102:Lectins; D014909:Wheat Germ Agglutinins