300 



INTRODUCTION TO ZOOLOGY. 



This is exemplified in the Ostrich (Figs. 237 249), and 

 in the Cassowary (Fig. 238). 



Fig. 233. CASSOWARY. 



Another peculiarity prevails in the birds just mentioned. 

 The breast-bone (sternum, Fig. 239) never presents the pro- 

 jecting ridge, or keel, which 

 we notice on the birds used 

 as food in these countries. 

 This keel serves an impor- 

 tant office, as it increases 

 the power of action in the 

 muscles by which the wing 

 is moved. It is large in 

 proportion to the power of 

 flight; but in birds which 

 cannot possibly fly, and 

 have only the rudiments 



Fig. 239. STERNUM, OR BREASTBONE.* of wings, the keel is alto- 

 gether wanting. 



* s, sternum : sc, scapula ; f, clavicle ; /*, keel ; c, coracoid ; r, sternal ribs. 



