Fig. 5. Representative serial cross sections from the epaxial muscles of a harbor seal Phoca vitulina stained for myosin heavy chain isoforms using a series of monoclonal antibodies. (A) Type I (slow-twitch, oxidative) fibers, (B) type IIa (fast-twitch, oxidative) fibers and (C) type IIb (fast-twitch, glycolytic) fibers. Lack of stain in C indicates an absence of type IIb fibers in this cross section of the muscle. Bar, 50 µm.