i 



SKELETON 



6S 



In the urodeles it is a short cartilaginous plate, lying mostly behind 

 the girdle, with its sides grooved to receive the medial ends of the 

 coracoids. In the toads (fig. 6s, A) and their allies (arcifera) it 

 has hardly passed beyond the urodele condition, but the hinder 

 angles are produced into long processes. In the frogs (firmisternia) 

 it consists of a slender thread between the medial ends of the girdles 

 (epicoracoids), but in front it expands into an omostemum, ossified 

 behind; while behind the girdle it forms a broad xiphistemum, the 

 anterior part of which is bone (fig. 63, B). 



Fig. 64. — Sternum, etc., of 

 Iguana iuberculata, after Blan- 

 chard. c, coracoid; cl, clavicle; 

 e, episternum; ec, epicoracoid; h, 

 humerus; pc, procoracoid; x, 

 xiphisternum. 



Fig. 65. — Sternum of guinea 

 pig. sr, sternal rib; si, sterne- 

 orje; vr, vertebral rib, «, xiphi- 

 sternum. 



In the lizards the sternum is a large rhomboid plate, largely 

 cartilaginous, sometimes perforated with two foramina and joined 

 by a varying number of ribs (fig. 64). In the crocodilia there is 

 an anterior rhombic plate, joined by two pairs of ribs and followed 

 by a second, so-called abdominal sternum, connected with from 

 five to seven pairs of ribs. Ichthyosaurs, plesiosaurs and snakes 

 have no sternum, while it was imperfectly ossified in theriomorphs 

 and dinosaurs. 



