Structure and Some Contractile Properties of Musculus Iliofibularis of Agama stellio stellio

The running speed of Agama stellio stellio was 2.1 ± 0.3 m s −1 at preferred body temperature (T b , 30°C). To account for sprint locomotion, we meaured two mechanical parameters and examined the ultrastructural features of a major locomotory muscle in normal walking and running locomotion, the iliofibularis muscle, which is considered to act as an extensor of the lower hind limb. The time to peak isometric twitch tension and time to half relaxation were 52 ± 7 ms and 76 ± 5 ms, respectively. The comparative ultrastructure of the fast and slow fibes provides structure‐to‐function correlation. The sarcoplasmic reticulum and T‐tubules system are abundant in fast fibres which serve to transmit Ca 2+ and spread the excitatory impulse intracellularly with great rapidity. In contrast, the membranous system of slow fibres is relatively poor and this indicates slow impulse propagation. Thus, these results show that the fast locomotion of Agama stellio stellio can, in part, be explained by the physiology and ultrastructure of the fibres of the locomotory muscles.