Fig. 4. Measurement schemes for feeding kinematic timing and angular variables in hagfish. (A) Gape cycle time is the elapsed time for maximal dental plate protraction and retraction. Time to maximum gape is the elapsed time to attain maximal dental plate protraction from a retracted position. Dental plate retraction time is the elapsed time to retract the dental plate from a maximally protracted position. Head depression time is the elapsed time from the onset to the completion of head depression. Head elevation time is the elapsed time from the onset to completion of head elevation from a maximally depressed state. (B) Kinematic angular variables defined. Lateral view of a hagfish with a maximally depressed head and a maximally protracted dental plate. Head depression angle (top) is the angle between the anterior tip of the snout before the onset of head depression (see light gray image), the pivoting point of the head, and the anterior tip of snout once the head is maximally depressed. Maximum protraction angle is the angle between the anterior tip of the snout, mouth opening and anterior tip of the maximally protracted dental plate.