The topographical organization and fiber types of extraocular muscle in mouse will be studied electronmicroscopically, with emphasis on the morphologically "slow" fibers and their innervation pattern. The extraocular muscles of mice inbred, respectively, for muscular dystrophy and myotonic dystrophy will be studied by combined light and electronmicroscopy for the detection of morphological changes associated with these degenerative disorders. Structural changes associated with oculomotor malfunction will be compared to those appearing in the affected peripheral musculature. Relationships will be sought between selective varieties of structural change and the respective types of muscle fibers. Histochemistry and morphology will be correlated on the same fibers within these muscles.