whatever may have been its function in the amphibians; and it was never large. It is known only in certain members of the Cotylosauria, Theromorpha, Dinocephalia, and Anomodontia, best developed perhaps of all in Diadectes and its allies of the Cotylosauria (Fig. 95), where its somewhat spatulate upper extremity partly overlies the front, upper border of the scapula, articulating below with the stem of the clavicle. It is vestigial in some forms and seems to be quite wanting in others. Among the Theromorpha it has been observed in Edaphosaurus (Fig. 98) as a rod-like bone at the upper front border of the scapula. In the Anomodontia and Dinocephalia (Fig. 107 d) it is a feeble splint, clearly a vestige. There have been several theories as to what has become of it, but none is demonstrable. Its vestigial condition in various cotylosaurs indicates its entire disappearance.
Fig. 97. Clavicles and interclavicle of Ophiacodon
(Theromorpha).
Clavicles. Clavicles are usually present in reptiles. They are absent in the Crocodilia, serpents, Mosasauria, and some Sauria; more or less vestigial in some lizards; and either absent or vestigial in the Pterosauria and Dinosauria.
In crawling reptiles (Figs. 96 b–99) they are usually curved bones, with a dilated mesial extremity, articulating on the ventral side of
