Figure 22. Functional morphology of jaw projection in a juvenile white sturgeon, Acipenser transmontanus. In the photograph, an individ-
ual is shown with the jaws near maximum projection and gape. The bottom four line drawings traced from high speed film, show
kinematics of jaw projection and the skeletal elements involved in jaw projection (based on ‘dimpling’ of the overlying skin and manip-
ulated incleared and double stained specimens). Jaw projection can be very rapid, and it involves at least three discrete stages: projection
itself (40msecs); adduction of the jaws (60msecs); and recovery of the jaws to the resting position (140 msecs and beyond). Also note that
opercular abduction occurs during the jaw recovery phase (arrows). h = hyomandibula; ih=interhyal; Ij = lower jaw; s = subopercle; uj = up-
per jaw.
martin jones
(Martin Jones)
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