Page:The Osteology of the Reptiles.pdf/149

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Interclavicle. The interclavicle in the earliest-known reptiles (Fig. 96 )

is an elongate bone with a dilated but not T-shaped anterior extremity. The stem underlies the approximated mesial borders of the coracoids, usually extending beyond them. In a specimen referred to Pantylus (Fig. 105), a primitive cotylosaur, the interclavicle is forked in front and somewhat fan-shaped behind, shaped very much like that of the monotremes. In the later cotylosaurs the front end is more dilated, as usual with all later reptiles. In the known forms of the Therapsida (Fig. 107 ) the shape is usually like that of the Theromorpha and Cotylosauria. It is very short and fan-shaped in Lystrosaurus of the Anomodontia (Fig. 94 ), where Broom attributes its reduction to water habits.