Expression patterns of CMVLacZ and TnILacZ1 transgenes in hindlimb crural muscles. Panels A-C show β-gal histochemistry of hindlimb muscle sections from adult transgenic mice of A) CMVLacZ line 18, B) TnILacZ1 line 29, C) CMVLacZ line 9. Panel D outlines muscles and muscle regions: S = soleus, P = plantaris, PALG = plantaris-adjacent lateral gastrocnemius, LG = lateral gastrocnemius, MG = medial gastrocnemius. The "complex zones" (regions containing all four fiber types) of the medial and lateral gastrocnemius are indicated by dashed lines. The superficial gastrocnemius includes LG and MG regions outside of the PALG and complex zones. The tissue block in panel A includes a piece of liver tissue (unstained) placed against the gastrocnemius muscle.