Histochemical Determination of the Fiber Composition of Locomotory Muscles in a Lizard, Dipsosaurus dorsalis

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A histochemical survey was done on the fiber composition of 12 different locomotory muscles in the lizard Dipsosaurus dorsalis. Three types of fibers were found in all muscles: (1) fast-twitch-glycolytic (FG); (2) fast-twitch-oxidative-glycolytic (FOG); and (3) tonic fibers. Virtually all locomotory muscles contain some tonic fibers. Most muscles have bulk white regions (containing mostly FG fibers) and distinct red, oxidative regions (with FOG and tonic fibers). These red regions are predominantly located around the joints in the hind limb muscles, and probably serve a postural and joint-stabilizing function. The predominance of FG fibers in the bulk white regions is well-correlated with the rapid, anaerobically supported predator escape behavior of D. dorsalis.