THE PECTORAL AND PELVIC GIRDLES 



127 



whatever may have been its function in the amphibians; and it was 

 never large. It is known only in certain members of the Cotylo- 

 sauria, Theromorpha, Dinocephalia, and Anomodontia, best devel- 

 oped 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 



Fig. 97. Clavicles and interclavicle of Ophiacodon 

 (Theromorpha). 



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 demon- 

 strable. Its vestigial condition in various cotylosaurs indicates its 

 entire disappearance. 



Clavicles. Clavicles are usually present in reptiles. They are ab- 

 sent 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 



