SKELETON 



117 



is retained in the lizards in a reduced condition (fig. 123). The 

 clavicle in turn is lost in chamaeleons and crocodiles, and if present 

 in the chelonians, it is represented by the epiplastron (p. 46), an ele- 

 ment of the carapace. The girdles are greatly reduced in the limbless 

 lizards and have vanished in the ophidians. 



In the BIRDS (fig. 60) the scapula is a sword-shaped bar over- 

 lying the ribs, while the coracoid extends from its junction with the 

 scapula at the glenoid fossa to the anterior end of the sternum. The 

 procoracoid has disappeared. The clavicles of the two sides are 



\A^. 



■-C 



s/ 



) r:SS^ 



Fig. 123 Ik,. 124. 



Fig. 123. — Sternum and pectoral girdle of Amblyrkynchus, after Steindacher. c, 

 coracoid; cl, clavicle; e, epicoracoid; es, episternum; h, humerus; m, mesocoracoid; ms, 

 mesoscapula; p, procoracoid; sc, scapula; s, sternum. 



KiG. 124. — Shoulder girdle of Ornithorhynchus. cl, clavicle; co, coracoid; «, epister- 

 num; g, glenoid fossa; pc, procoracoid; s, scapula; st, sternum. 



united at their medial or ventral ends to form the well-known furcula 

 (wishbone) which may articulate with the sternum between the two 

 coracoids, or, with diminishing powers of flight, may end freely 

 below. 



MAMMALS. — The shoulder girdle of the monotremes (fig. 124) 

 is strikingly like that of lizards, the coracoids acting as a brace be- 

 tween sternum and glenoid fossa, while the resemblance is strength- 

 ened by the presence of the episternum. This same large develop- 

 ment of the coracoids occurs in the young of some marsupials, but 

 in the adults, as in the rest of the mammals, the coracoid is greatly 



