The Evolution of the Mitochondria-to-Calcium Release Units Relationship in Vertebrate Skeletal Muscles
Figure 4
Longitudinal sections of leg muscles from a small lizard, as an example from reptiles. The myofibrils are small, and the CRUs (triads) are frequent, as expected from a rapid muscle. Mitochondria are not frequent, and they are located in single longitudinal rows between the myofibrils. An occasional proximity to CRU occurs when the mitochondria cross the T tubule network (arrows, see also Figures 3 and 5 for birds and amphibia).
