284 



INTEODUCTION TO ZOOLOGY. 



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

 the Cassowary {Fig. 238). 



Fig. 238.— Cassowart. 



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 ofl&ce, 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 of wings, 

 the keel is altogether want- 

 ing. 



Fig. 239.— Stebnuk, ob Bueast-iione.* 



* $, sternum ; «c, scapula ; f, clavicle ; Jc, keel ; c, coracoid ; r, sternal ribs. 



