. Bulletin. Natural history. RUSSELL: AMERICAN MOSASAURS 41 mandibulae extemus profundus. In Plotosaiinis, TyJosaurus and Prognalhodon it is overlapped medially by a more ventral tongue from the parietal. Posteriorly the supratemporal is poorly exposed behind the paroccipital process and under the suspensorial ramus of the parietal in Clidastes, Mosasaurus, Platecarpus and Tylosaurus. It seems quite likely that the pars transversalis capitis of the M. longissimus capitis originated on the vertical notch lying be- tween the distal end of the paroccipital process and the supratemporal and that f
. Bulletin. Natural history. RUSSELL: AMERICAN MOSASAURS 41 mandibulae extemus profundus. In Plotosaiinis, TyJosaurus and Prognalhodon it is overlapped medially by a more ventral tongue from the parietal. Posteriorly the supratemporal is poorly exposed behind the paroccipital process and under the suspensorial ramus of the parietal in Clidastes, Mosasaurus, Platecarpus and Tylosaurus. It seems quite likely that the pars transversalis capitis of the M. longissimus capitis originated on the vertical notch lying be- tween the distal end of the paroccipital process and the supratemporal and that fibers of the pars articuloparietalis of the M. longissimus capitis originated only along the posterior rim of the parietal, as they do in Varanus. The M. depressor mandibulae may have lacked an origin on the supratemporal in mosasaurs, al- though this is a major site of attachment of this muscle in Varanus, Pterygoid Units The pterygoid units are composed of the pterygoids and ectopterygoids. They link the ventromedial corners of the quadrates (quadrate units), the basipterygoid processes (occipital unit), and the base of the epipterygoids (epipterygoid units) with a long bar of bone to brace the jugal and palatines (muzzle unit) anteriorly. Through these bones longitudinal motion from the ventral portion of the occipital unit is transmitted to the posteroventral edge of the muzzle Text-fig. 20. Left quadratic suspensorium of Platecarpus (AMNH 1820, X V4). PTERYGOID The pterygoid in mosasaurs inay perhaps be best considered as composed of a central, anteroposterior body with two large diverging processes, one antero- laterally to the ectopterygoid and another posterolaterally to the medial edge of the quadrate. The pterygoids do not meet along the midline of the skull, al- though the incisura piriformis is narrower than in Varanus. The main body of the pterygoid is a short, dorso\entrally flattened column, terminating posteriorly in a tongue-shaped wing (basisphenoid pro
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