366 



BONES OF THE TRUNK OF BIRDS. 



generally larger than the others, and elevated into a projecting 

 crest. 



328. The ribs of Birds also present some peculiarities of 

 structure, which tend to give solidity to the thorax. The car- 

 tilage, which in the Mammalia fixes them to the sternum, is 

 here replaced by a bone ; and each of them is provided in the 

 middle with a flattened process, which is directed obliquely 

 backwards above the next rib ; so that all these bones have 

 points of support on one another. But the most remarkable 

 part of the osseous structure is the sternum ; which, as it gives 

 insertion to the muscles of flight, presents in Birds a very high 

 development, and constitutes a sort of convex buckler, usually 

 square, which covers the thorax and a large part of the abdomen. 



FIG. 179- SKELETON OF OSTIUCH. 



In the Cassowary and Ostrich, which cannot rise in the air, and 

 which have only rudimentary wings, the sternum does not present 



