The Evolution of the Mitochondria-to-Calcium Release Units Relationship in Vertebrate Skeletal Muscles
Figure 5
Images from the frog gastrocnemius (a) and sartorius (b) in longitudinal sections. The predominant location of mitochondria is similar to that of birds and reptiles, again providing limited contacts with CRUs. Note overall scarcity of mitochondria in these muscles gastrocnemius. Others have more frequent mitochondria but still no large clusters at the periphery.
