254 



VERTEBRATE SKELETON 



precoracoid) in front, such as occurs in lizards, while the lateral end of the 

 coracoid has two facets for articulation with scapula and humerus. The 

 T-shaped episternum is small. 



Sauropterygia (fig. 269), like many other aquatic vertebrates, have the 

 scapula reduced to a small plate with a strong oblique dorsal process. In 

 the latest Plesiosaurs the bone has disappeared except in the glenoid region, 



Fig. 269. — A to C, development of pectoral girdle of Cryptodeidus (Andrews, in 

 Woodward); D, girdle of Lariosaurus (Deeke, '86). co, coracoid; cl, clavicle; p, pre- 

 sternum or episternum; sc, scapula. In A to C, note relative decrease in size of clavicle 

 and meeting of coracoids of the two sides 



from which a descending process connects with the somewhat rudimentary 

 secondary girdle, a process which some compare with the anterior bar of 

 Chelonians, the nearest relatives of the Sauropterygia. In more recent 

 genera the coracoid, which has a rather broad median margin, has a pecuhar 

 antero-laterally directed process, and a broad space between this and the clavicles 

 which may have been occupied by a precoracoid. Still others had a small 



Fig. 270. — Pectoral girdle and sternum of Ornithostoma (Williston, '97). c, caracoid; 

 h, humerus; sc, scapula; st, sternum. 



precoracoid reaching a triangular episternum and fused laterally with the 

 scapula. The clavicles connect by suture with the scapula. 



DiNOSAURiA have a large scapula, strong and usually elongate, and often 

 connected or even fused with the small coracoid plate which is rounded in front 

 and has a foramen near the glenoid fossa. Apparently clavicles and precoracoids 

 are lacking; no episternum is known and the sternum is possibly represented by a 

 pair of ossifications, not known in Theropoda. 



