Whole mounts of adult muscle were stained with antibodies to myosin heavy chain (MHC) and GFP. Cross-sections of muscle were stained with antibodies to Laminin. (A) Intercostal muscle fibers normally extend from one rib to the adjacent rib (arrows) but extend and cross over one or more ribs in Abl2 mutant mice. (B) Muscle fibers in the levator auris muscle appear wavy in Abl2 mutant mice. Moreover, the midline tendon, marked by Scx::GFP, is reduced in size (double headed arrows). (C) Muscle fibers in the diaphragm muscle remain longer and the central tendon is reduced in size in adult Abl2 mutant mice. (D) The cross-sectional area of myofibers in adult, 8 week old, Abl2−/− mice is normal. Scale bar is 250 µm in A and B, and 50 µm in D.