Fig. 7. The effect of sarcomere length and tendon morphology on active and passive force production in the anterior division of the adductor mandibula of the ratfish. Sarcomere length is estimated from predicted muscle strains during jaw opening (see Fig. 5) and a resting length of 2.0 µm. In the untwisted condition (A,B), passive tension increases more rapidly in the anterior face than in the posterior face as the jaw is opened (A). This results in the two portions of the muscle beginning their active tension generation at disparate points on their active curves (B) and having heterogeneous force production capabilities, lowering the whole muscle force output at prey contact. In contrast, the faces of the muscle in the twisted condition (C,D) occupy similar portions on both their active (D) and passive (C) tension curves, allowing more optimal active tension generation and a wider gape without the detrimental effects of high passive tension forces.