484 



ORDER V._ CURSORES. 



436. IN the Birds of this order, we have a marked excep- 

 tion to the general type of the class. We are accustomed to 

 think of Birds as denizens of the air, as endowed with the 

 powers of flight ; but the Ostrich and its allies, of which this 

 order consists, are exclusively terrestrial. They have wings, it 

 is true ; but these organs are but little developed, and are totally 

 incapable by their most energetic action, of raising the Birds 

 from the ground. The utmost that they can accomplish, is to 

 assist the powerful run, which is effected by the strong and 

 highly-developed legs. The whole locomotive energy is thrown 

 into the posterior extremities, the bones of which are large and 

 stout, and the muscles acting upon them exceedingly voluminous. 

 These Birds all agree in the flatness of the sternum, which is 

 entirely destitute of projecting keel (Fig. 274) ; and the pee- 



Fro. 274. STERNUM OF EMEU. 



toral muscles which arise from it are extremely thin. In many 

 points of their conformation they approach Mammalia; thus 

 we find in the Ostrich a partial diaphragm, which is still 

 more completely developed in the Apteryx; and the ureters 

 meet in a sort of urinary bladder, instead of emptying them- 

 selves at once into the cloaca ( 346). It is not only in the 



