Fig. 4. Details of the sonic muscle insertion on the swimbladder in Carapus boraborensis. (A) Micrograph of the anterior face of the swimbladder illustrating the tubercles that anchor the tendon hooks at rest. (B) Micrograph of the complex sonic muscle tendon (anterior is toward the bottom) illustrating the hook and connective tissue, which attach to the swimbladder. (C,D,E) Frontal sections of the anterior part of the swimbladder illustrating the tubercles that anchor the tendon hooks. CT, connective tissue; SWB, swimbladder; Tb, tubercule; black arrows, tissue of the swimbladder fenestra. Scale bars, 50 µm.