248 



VERTEBRATE SKELETON 



largely calcifying or ossifying as a suprascapula (fig. 262). The 

 distinct coracoid enters the glenoid fossa, the epicoracoid usually 

 remains cartilage. The precoracoid (fig. 263) is pecuHar in being 

 largely or wholly replaced by the clavicle which grows over it from 

 in front, so that it may persist as cartilage within the clavicle, may 

 coossify with that bone, or may entirely disappear, except that parts 



Fig. 262. — Pectoral girdle of Rana tetnporaria (Parker, '63). cf, coracoid fenestra; 

 cl, clavicle; co, coracoid; e, epicoracoid; g, glenoid fossa; m, mesosternum; pc, precora- 

 coid; 5, scapula; 55, suprascapula; x, xiphisternuin. 



may persist as cartilage at either end of the clavicle in many frogs. 

 The clavicles, the only membrane bones in the girdle, meet in the 

 middle line, but do not enter the glenoid fossa. No true episternum 

 is present, but in most Anura a pair of cartilages in front of the girdle 

 ossify as a single bone of uncertain homology. This has been called 



Fig. 263. — Two stages in development of pectoral girdle of Rana esculenta (Goette, 

 '77). c, clavicle; co, coracoid; e, episternum; g, glenoid fossa; p, precoracoid; s, base of 

 scapula. 



omostemttm and prestemiim, earher episternum; it certainly is not 

 the latter. 



REPTELIA with a few exceptions (snakes and some footless 

 lizards) have a pectoral girdle. Unfortunately httle is known of the 

 girdle of the ancestral group, the Theromorphs, and nothing concern- 



