The fine structural differences of motor endplate among the red, white and intermediate muscle fibers of the rat fast limb muscle, M. extensor digitorum longus, were observed by the electron microscope. The motor endplate of the red fiber was small. The junctional folds were poorly developed and their number was small. In the white fiber, the motor endplate was large and the junctional folds were well developed and their number was far more numerous than those in the red fiber. In the intermediate fiber, the development of junctional folds of motor endplate was rather similar to that of the white fiber although the number of the junctional folds was a little less than that of the white fiber. © 1969, Tohoku University Medical Press. All rights reserved.
