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Fig. 1. Action of the sternohyoideus (SH) in medial (A) and ventral (B) views. (A)
The SH originates on posterior myosepta and the pectoral girdle. Thick
ligaments connect the urohyal to the hyoid structure, so that the primary
action of the sternohyoideus is to rotate the hyoid about its articulation on
the suspensioria, depressing the buccal floor away from the neurocranium and
expanding the buccal cavity. Ventral rotation of the hyoid results in
depression of the lower jaw through a linkage between the proximal ends of the
hyoid and the mandible. (B) Caudal movement also widens the midventral angle
of the hyoid, rotating the suspensoria laterally from the neurocranium and
laterally expanding the buccal cavity.