Hyostyly

the articulation of the jawbone with the skull in most sharks and rays. In hyostyly, the rear end of the primary upper jaw is attached to the auditory area of the skull only by the upper (hyomandibular) section of the hyoid arch. In the front part, the jaw remains free or is joined to the skull by means of ligaments. In sharks the suspensorium is formed by a single massive cartilage, while in rays it is divided into two independent bone formations, the suspensorium itself (hyomandibular) and a small connecting bone (symplectic bone). Hyostyly increases the jaw’s mobility but does not assure sufficient durability. In fish with jaws of the crushing type, hyostyly is usually replaced by amphistyly or auto-styly.