SAURO PTERYGIA 



81 



quite certain because of the very broad expanse of the coracoids, 

 between the articulations of the front legs. 



The shoulder girdle or pectoral arch is strangely unlike that of 

 any other reptiles. There is no breast bone, since the breast bone 



Fig. 35. — Pectoral girdle of Trinacromerum from above: ic, interclavicle; cl, 

 clavicle; sc, scapula; c, coracoid. 



is a comparatively late development in reptiles, not appearing, 

 probably, until after the plesiosaurs had begun their existence. 

 Taking the place of the sternum, the very large and broad coracoids 



