io8 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



lost in chamseleons and crocodiles, and if present in the chelonians, it is 

 represented by the epiplastron (p. 41), an element of the carapace. 

 The girdles are greatly reduced in the limbless lizards and have van- 

 ished in the ophidians. 



In the BIRDS (fig. 53) the scapula is a sword-shaped bar overlying 

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

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

 of the two sides are 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. 





, 



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FIG. 112. FIG. 113 



FIG. 112. Sternum and pectoral girdle of Amblyrhynchus, after Steindacher. c, 

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

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



FIG. 113. Shoulder girdle of Ornithorhynchus. cl, clavicle; co, coracoid; e, epister- 

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



MAMMALS. The shoulder girdle of the monotremes is strikingly 

 like that of lizards, the coracoids acting as a brace between sternum and 

 glenoid fossa, while the resemblance is strengthened by the presence of 

 the episternum. This same large development 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 reduced, persisting only as a small 

 projection, the coracoid process, anchylosed to the ventral end of the 



