498 THE MECHANICAL FUNCTIONS. 



being anchylosed together for this purpose ; so 

 that they form a bone of great length. The coccy- 

 geal vertebrae (q) are also numerous ; but they are 

 compressed into a small space, and enjoy great lati- 

 tude of motion, being subservient to the movements 

 of the tail. 



The ribs are numerous, and of considerable 

 strength : they send out processes, which are di- 

 rected backwards, passing over the next rib before 

 they terminate, and giving very effectual support to 

 the walls of the chest. The ribs are continued along 

 the abdomen, and afford protection to the viscera 

 in that cavity ; and some arise even from the 

 sacrum, and from the iliac bones. Those which are 

 in front are united to the sternum (s) by means of 

 sternal appendices, which are ossified, and appear 

 as the continuations of the ribs, or as if the ribs 

 were jointed in the middle. 



The sternum is of enormous size, extending over 

 a considerable part of the abdomen, and having a 

 large perpendicular crest descending, like the keel 

 of a ship, from its lower surface. The object of 

 this great developement is to furnish extensive at- 

 tachment to the large pectoral muscles employed 

 to move the wings, and which, taken together, are 

 generally heavier than the rest of the body. Con- 

 sidered with reference to all the other muscles, and 

 to the weight of the body itself, these pectoral 

 muscles are of enormous strength. The flap of a 

 swan s wing is capable of breaking a man's leg ; 

 and a similar blow from an eagle has been known 

 to be instantly fLital. The bat is the only instance, 

 among the mammalia, where the sternum presents 

 this peculiar carinated, or keel-like shape ; and the 



