STERNUM 



55 



In apodal lizards the sternum is reduced, (even absent) and usually 

 is not connected with the ribs. Sometimes it is continued far back 



Fig. 6i.- 



-Pectoral girdles and sterna of (.4) Phrynosoma (Fiirbringer, 'oo); {B) Agama 

 (Siebenrock, '95) and (C) Chirotes canaliculatus (Parker, '68). 



Pythonomorphs 



as a pair of parallel xiphisternal bars (fig. 6i 

 have a triangular unossified sternum. 



The sternum of recent Crocodilia (calcified 

 cartilage) has the three parts — manubrium, 

 meso- and xiphisternum, the first quadrate in 

 outline with an episternum on its ventral 

 surface (fig. 62). The mesosternal bars may 

 be largely separate, or may unite through- 

 out. In most species the xiphisternal parts 

 diverge, but in Caiman they are united 

 distally. 



Characteristic of reptiles is another sternal 

 element, the episternum or interclavicle, a 

 membrane bone which shows no trace of being 

 a paired structure. It lies on the ventral 

 side of the sternum and connects laterally 

 with the clavicles of the two sides. Its shape 

 varies greatly (figs. 61, 62, 265) being a longitudinal or transverse 



Fig. 62. — Sternum and 

 pectoral girdle of Crocodilus 

 acutus just before hatching 

 (W. K. Parker, '68). c, 

 coracoid; e, episternum; ec,? 

 epicoracoid; g, glenoid fossa; 

 m, mesosternum; p, pres- 

 ternum; s, scapula; x, 

 xiphisternum. 



