132 



STORY OF THE REPTILES 



usually reaching the breast-bone Avhen that is pres- 

 ent. In many ancient forms the ribs appear short, 

 and there is no evidence of a breast-bone. In croco- 

 dilians and Tuatera the ribs have, near the middle, 

 projections or flat blunt spurs (uncinate processes) 

 which reach back and lap over the next rib, thus 

 strengthening the bony cage. The lower birds also 

 have this. 



In tortoise-forms the ribs are usually fused into 

 the shell and are broad and flattened. In one case, 



Fig. 61.— Tortoise-shell turtle (hawkbill) ( Eretmochelys imbrkata). 



however, the sea-turtle (Sj^hargis), the ribs are free 

 from the shell but much flattened. It has been claimed 

 that the tortoise-forms have no true ribs, but that 

 those apparent are merely the spiny projections of the 



